SEARS MUNICIPAL TRUST DELAWARE PORTFOLIO SERIES 12
485BPOS, 1997-06-26
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                         National Portfolio Series 126
                                     File No. 33-49221
                          Delaware Portfolio Series 12
                                     File No. 33-47084
                   Investment Company Act No. 811-3676


    SECURITIES AND EXCHANGE COMMISSION
         WASHINGTON, D.C.  20549
   
      POST-EFFECTIVE AMENDMENT NO. 4
               TO FORM S-6
    

For Registration Under the Securities Act of 1933 of Securities of Unit
Investment Trusts Registered on Form N-8B-2.

   A.   Exact name of Trust:

        DEAN WITTER SELECT MUNICIPAL TRUST,
        NATIONAL PORTFOLIO SERIES 126
        DELAWARE PORTFOLIO SERIES 12

   B.   Name of Depositor:

        DEAN WITTER REYNOLDS INC.

   C.   Complete address of Depositor's principal executive
        office:

        DEAN WITTER REYNOLDS INC.
        Two World Trade Center
        New York, New York  10048

   D.   Name and complete address of agents for service:

        Mr. Michael D. Browne
        Dean Witter Reynolds Inc.
        Unit Trust Department
        Two World Trade Center - 59th Floor
        New York, New York  10048

        Copy to:

        Kenneth W. Orce, Esq.
        Cahill Gordon & Reindel
        80 Pine Street
        New York, New York  10005

        Check box if it is proposed that this filing should
        become effective immediately upon filing pursuant to
        paragraph (b) of Rule 485.
        Pursuant to Rule 429(b) under the Securities Act of
        1933, the Registration Statement and prospectus
        contained herein relates to Registration Statements
        Nos.:

   33-49221
   33-47084
                    Cross Reference Sheet

 Pursuant to Rule 404(c) of Regulation C
     under the Securities Act of 1933

         (Form N-8B-2 Items required by Instruction 1
      as to Prospectus on Form S-6)


Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


   I.  Organization and General Information


 1.  a)  Name of Trust                   Front Cover
     b)  Title of securities issued

 2.  Name and address of Depositor       Table of Contents

 3.  Name and address of Trustee         Table of Contents

 4.  Name and address of principal       Table of Contents
     Underwriter

 5.  Organization of Trust               Introduction

 6.  Execution and termination of        Introduction; Amendment     
     Indenture                           and Termination of the 
                                         Indenture

 7.  Changes of name                     *30

 8.  Fiscal Year                         Included in Form N-8B-2

 9.  Litigation                          *30

   II.  General Description of the Trust
        and Securities of the Trust     


10.  General Information regarding
     Trust's Securities and Rights of
     Holders

   a)  Type of Securities              Rights of Unit Holders
       (Registered or Bearer)


______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


   b)  Type of Securities              Administration of the
        (Cumulative or                 Trust-Distribution
        Distributive)

   c)  Rights of Holders as to         Redemption; Public
       Withdrawal or Redemption        Offering of Units Secondary
                                       Market

   d)  Rights of Holders as to         Public Offering of Units-
        conversion, transfer, etc.     Secondary Market;
                                       Exchange Option;
                                       Redemption; Rights of
                                       Unit Holders-Certificates

   e)  Lapses or defaults with         *30
        respect to periodic payment
        plan certificates

   f)  Voting rights as to             Rights of Unit Holder-
        Securities under the           Certain Limitations
        Indenture

   g)  Notice to Holders as to         Amendment and Termination
        change in                      of the Indenture

        1)  Assets of Trust            Administration of the
                                       Trust-Reports to Unit
                                       Holders; The Trust-
                                       Summary Description of
                                       the Portfolios

        2)  Terms and Conditions of    Amendment and Termination
            Trust's Securities        of the Indenture

        3)  Provisions of Trust        Amendment and Termination
                                       of the Indenture

        4)  Identity of Depositor      Sponsor; Trustee
            and Trustee

   h)  Security Holders Consent
       required to change

        1)  Composition of assets      Amendment and Termination
            of Trust                  of the Indenture

______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


        2)  Terms and conditions of    Amendment and Termination
            Trust's Securities        of the Indenture

        3)  Provisions of Indenture    Amendment and Termination
                                      of the Indenture

        4)  Identity of Depositor      *30
            and Trustee

     i)  Other Provisions              Cover of Prospectus; Tax
                                       Status

11.  Type of securities comprising       The Trust-Summary
     units                               Description of the
                                         Portfolios; Objectives
                                         and Securities Selection;
                                         The Trust-Special
                                         Considerations

12.  Type of securities comprising       *30
     periodic payment certificates

13.  a)  Load, fees, expenses, etc.     Summary of Essential
                                        Information; Public
                                        Offering of Units- Public
                                        Offering Price; -Profit
                                        of Sponsor; -Volume
                                        Discount; Expenses and
                                        Charges

   b)  Certain information             *30
        regarding periodic payment
        certificates

   c)  Certain percentages             Summary of Essential
                                       Information; Public
                                       Offering of Units-Public
                                       Offering Price; -Profit
                                       of Sponsor; -Volume
                                       Discount

   d)  Price differentials             Public Offering of
                                       Units-Public Offering
                                       Price


______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


   e)  Certain other loads, fees,      Rights of Unit Holders-
        etc. payable by holders        Certificates

   f)  Certain profits receivable      Redemption-Purchase by
        by depositor, principal        the Sponsors of Units
        underwriters, trustee or       Tendered for Redemption
        affiliated persons

   g)  Ratio of annual charges to      *30
        income

14.  Issuance of trust's securities      Introduction; Rights of
                                         Unit Holders-Certificates

15.  Receipt and handling of payments    Public Offering of Units-
     from purchasers                     Profit of Sponsor

16.  Acquisition and disposition of      Introduction; Amendment
     underlying securities               and Termination of the
                                         Indenture; Objectives and
                                         Securities Selection; The
                                         Trust-Summary Description
                                         of the Portfolio;
                                         Sponsor-Responsibility

17.  Withdrawal or redemption by         Redemption; Public
     Security Holders                    Offering of Units-
                                         Secondary Market

18.  a)  Receipt and disposition of      Administration of the
         income                         Trust; Reinvestment
                                        Programs

   b)  Reinvestment of                 Reinvestment Programs
        distributions

   c)  Reserves or special fund        Administration of the
                                       Trust-Distribution

   d)  Schedule of distribution        *30

19.  Records, accounts and report        Administration of the
                                        Trust-Records and
                                        Accounts;-Reports to Unit
                                        Holders

______________________

*    30 Not applicable, answer negative or not required.
Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


20.  Certain miscellaneous provisions    Amendment and Termination
     of the Indenture                    of the Indenture;
                                         Sponsor-Limitation on
                                         Liability-Resignation;
                                         Trustee-Limitation on
                                         Liability-Resignation

21.  Loans to security holders           *30

22.  Limitations on liability            Sponsor, Trustee;
                                         Evaluator-Limitation on
                                         Liability

23.  Bonding arrangements                Included in Form N-8B-2

24.  Other material provisions of the    *30
     Indenture

   III.  Organization Personnel and
         Affiliated Persons of Depositor


25.  Organization of Depositor           Sponsor

26.  Fees received by Depositor          Expenses and Charges-
                                         Fees; Public Offering of
                                         Units-Profit of Sponsor

27.  Business of Depositor               Sponsor and Included in
                                         Form N-8B-2

28.  Certain information as to           Included in Form N-8B-2
     officials and affiliated persons
     of Depositor

29.  Voting securities of Depositor      Included in Form N-8B-2

30.  Persons controlling Depositor       *30

31.  Payments by Depositor for           *30
     certain other services

32.  Payments by Depositor for           *30
     certain other services rendered
     to trust

______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


33.  Remuneration of employees of        *30
     Depositor for certain services
     rendered to trust

34.  Remuneration of other persons        *30
     for certain services rendered to     trust

   IV.  Distribution and Redemption of Securities


35.  Distribution of trust's             Public Offering of Units
- -    securities by states                Public Distribution

36.  Suspension of sales of trust's      *30
     securities

37.  Revocation of authority to          *30
     distribute

38.  a)  Method of distribution          Public Offering of Units
     b)  Underwriting agreements
     c)  Selling agreements

39.  a)  Organization of principal       Sponsor
         underwriter
     b)  N.A.S.D. membership of
         principal underwriter

40.  Certain fees received by            Public Offering of Units-
     principal underwriter               Profit of Sponsor

41.  a)  Business of principal           Sponsor
         underwriter
     b)  Branch offices of principal     *30
         underwriter
     c)  Salesman of principal           *30
         underwriter

42.  Ownership of trust's securities     *30
     by certain persons

43.  Certain brokerage commissions       *30
     received by principal
     underwriter

______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


44.  a)  Method of valuation             Public Offering of Units

     b)  Schedule as to offering         *30
         price

   c)  Variation in offering price     Public Offering of Units-
        to certain persons             Volume Discount; Exchange
                             option

45.  Suspension of redemption rights     *30

46.  a)  Redemption valuation            Public Offering of Units-
                                         Secondary Market;
                                         Redemption

   b)  Schedule as to redemption       *30
        price

47.  Maintenance of position in          See items 10(d), 44 and
     underlying securities               46

   V. Information concerning the Trustee or Custodian


48.  Organization and regulation of      Trustee
     Trustee

49.  Fees and expenses of Trustee        Expenses and Charges

50.  Trustee's lien                      Expenses and Charges

   VI.  Information concerning Insurance
        of Holders of Securities         


51.  a)  Name and address of             *30
         Insurance Company

   b)  Type of policies                *30

   c)  Type of risks insured and       *30
        excluded

   d)  Coverage of policies            *30


______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


   e)  Beneficiaries of policies       *30

   f)  Terms and manner of             *30
        cancellation

   g)  Method of determining           *30
        premiums

   h)  Amount of aggregate premiums    *30
        paid

   i)  Who receives any part of        *30
        premiums

   j)  Other material provisions of
        the Trust relating to          *30
        insurance

   VII.  Policy of Registrant


52.  a)  Method of selecting and         Introduction; Objectives
        eliminating securities from      and Securities Selection;
        the Trust                        The Trust-Summary
                                         Description of the
                                         Portfolio Sponsor-
                                         Responsibility

   b)  Elimination of securities       *30
        from the Trust

   c)  Policy of Trust regarding       Introduction; Objectives
        substitution and               and Securities Selection;
        elimination of securities      Sponsor-Responsibility;

   d)  Description of any              30
        fundamental policy of the
        Trust

53.  Taxable status of the Trust         Cover of Prospectus; Tax
                                         Status

   VIII.  Financial and Statistical Information



______________________

*    30 Not applicable, answer negative or not required.

Form N-8B-2                              Form S-6
Item Number                              Heading in Prospectus


54.  Information regarding the           *30
     Trust's past ten fiscal years

55.  Certain information regarding       *30
     periodic payment plan
     certificates

56.  Certain information regarding       *30
     periodic payment plan
     certificates

57.  Certain information regarding       *30
     periodic payment plan
     certificates

58.  Certain information regarding       *30
     periodic payment plan
     certificates

59.  Financial statements                Statement of Financial
     (Instruction 1(c) to Form S-6)      Condition





______________________

*    30 Not applicable, answer negative or not required.
          LOGO

DEAN WITTER SELECT
MUNICIPAL TRUST

NATIONAL PORTFOLIO SERIES 126

DELAWARE PORTFOLIO SERIES 12

(Unit Investment Trusts)


_______________________________________________________________

These Trusts were formed for the purpose of providing interest
income which in the opinion of bond counsel is, under existing
law, excludable from gross income for Federal income tax purposes
(except in certain instances depending on the Unit Holders) and,
in the case of the Delaware Trust only, is exempt from State of
Delaware income taxes to individual Unit Holders resident in the
State of Delaware, through investment in a fixed portfolio
consisting primarily of investment grade long-term state,
municipal and public authority debt obligations.  The value of the
Units of each of the Trusts will fluctuate with the value of the
portfolio of underlying Securities.  Minimum Purchase:  1 Unit.
_______________________________________________________________

This Prospectus consists of two parts.  Part A contains a Summary
of Essential Information and descriptive material relating to the
Trusts, and the portfolio and financial statements of each Trust.
Part B contains a general description of the Trusts.  Part A may
not be distributed unless accompanied by Part B.
_______________________________________________________________

The Initial Public Offering of Units in the Trusts has been
completed.  The Units offered hereby are issued and outstanding
Units which have been acquired by the Sponsor either by purchase
from the Trustee of Units tendered for redemption or in the
Secondary Market.
_______________________________________________________________

Sponsor:    LOGO             DEAN WITTER REYNOLDS INC.
_______________________________________________________________

THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES
COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION OR ANY
STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY
OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.
_______________________________________________________________

Read and retain both parts of this Prospectus for future
reference.

Units of the Trusts are not deposits or obligations of, or
guaranteed or endorsed by, any bank, and the Units are not
federally insured by the Federal Deposit Insurance Corporation,
Federal Reserve Board, or any other agency.

   
 Prospectus Part A dated June 26, 1997    
 
THIS PROSPECTUS DOES NOT CONTAIN ALL OF THE INFORMATION WITH
 RESPECT TO THE INVESTMENT COMPANY SET FORTH IN ITS REGISTRATION
 STATEMENT AND EXHIBITS RELATING THERETO WHICH HAVE BEEN FILED
 WITH THE SECURITIES AND EXCHANGE COMMISSION, WASHINGTON, D.C.,
 UNDER THE SECURITIES ACT OF 1933 AND THE INVESTMENT COMPANY ACT
 OF 1940, AND TO WHICH REFERENCE IS HEREBY MADE.

     DEAN WITTER SELECT MUNICIPAL TRUST
        NATIONAL PORTFOLIO SERIES 126
        DELAWARE PORTFOLIO SERIES 12


              TABLE OF CONTENTS

 PART A                                                    Page

   
 Table of Contents...................................     A-1
 Summary of Essential Information....................     A-3
 The National Trust..................................     A-9
 The Delaware Trust..................................    A-11
 Independent Auditor's Report........................     F-1
    
 PART B

 Introduction........................................        1
 The Trust...........................................        2
     Special Considerations .........................        2
     Summary Description of the                              3
       Portfolios ...................................
 Insurance on the Securities                                21
   in an Insured Trust...............................
 Objectives and Securities Selection.................       25
 The Units...........................................       26
 Tax Status..........................................       27
      Public Offering of Units.......................       32
      Public Offering Price..........................       32
      Public Distribution............................       33
      Secondary Market...............................       34
      Profit of Sponsor..............................       35
      Volume Discount................................       35
 Exchange Option.....................................       36
 Reinvestment Programs...............................       37
 Redemption..........................................       38
      Tender of Units................................       38
      Computation of Redemption Price
        per Unit.....................................       39
      Purchase by the Sponsor of Units
        Tendered for Redemption......................       39
 Rights of Unit Holders..............................       40
      Certificates...................................       40
      Certain Limitations............................       40
                     A-1
 Expenses and Charges................................       40
      Initial Expenses...............................       40
      Fees...........................................       40
      Other Charges..................................       41
 Administration of the Trust.........................       42
      Records and Accounts...........................       42
      Distribution...................................       42
      Distribution of Interest and
        Principal....................................       42
      Reports to Unit Holders........................       44
 Sponsor.............................................       45
 Trustee.............................................       47
 Evaluator...........................................       48
 Amendment and Termination
   of the Indenture..................................       49
 Legal Opinions......................................       50
 Auditors............................................       50
 Bond Ratings........................................       50
 Federal Tax Free vs. Taxable
   Income............................................       54


                  Sponsor:

          Dean Witter Reynolds Inc.
           Two World Trade Center
          New York, New York  10048

                 Evaluator:

        Kenny S&P Evaluation Services
     A Division of J.J. Kenny Co., Inc.
                 65 Broadway
          New York, New York  10006

                  Trustee:
   
          The Chase Manhattan Bank
               270 Park Avenue
          New York, New York  10017
    
 NO PERSON IS AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
 REPRESENTATIONS WITH RESPECT TO THIS INVESTMENT COMPANY NOT
 CONTAINED IN THIS PROSPECTUS; AND ANY INFORMATION OR
 REPRESENTATION NOT CONTAINED HEREIN MUST NOT BE RELIED UPON AS
 HAVING BEEN AUTHORIZED.  THIS PROSPECTUS DOES NOT CONSTITUTE AN
 OFFER TO SELL, OR A SOLICITATION OF AN OFFER TO BUY, SECURITIES
 IN ANY STATE TO ANY PERSON TO WHOM IT IS NOT LAWFUL TO MAKE
 SUCH OFFER IN SUCH STATE.



                     A-2
<PAGE>
<TABLE>
<CAPTION>

                                     SUMMARY OF ESSENTIAL INFORMATION
                                                     
                                    DEAN WITTER SELECT MUNICIPAL TRUST
                                      NATIONAL PORTFOLIO SERIES 126
                                                     
                                           As of April 30, 1997



<S>                                <C>                <S>                                       <C>

FACE AMOUNT OF SECURITIES           $3,805,000.00     DAILY RATE AT WHICH ESTIMATED NET
                                                        INTEREST ACCRUES PER UNIT               .0155%
                                                      
NUMBER OF UNITS                             3,797     ESTIMATED CURRENT RETURN (based on
                                                        Public Offering Price)<F2>              5.470%
FRACTIONAL UNDIVIDED INTEREST IN THE                  
  TRUST REPRESENTED BY EACH UNIT        1/3,797th     ESTIMATED LONG TERM RETURN (based on
                                                        Public Offering Price)<F2>              5.407%
                                                      
PUBLIC OFFERING PRICE                                 
                                                      MONTHLY INTEREST DISTRIBUTIONS
  Aggregate bid side evaluation                       
    of Securities in the Trust      $3,690,150.00       Estimated net annual interest rate
                                                          per Unit times $1,000                 $56.06
  Divided by 3,797 Units            $      971.86       Divided by 12                           $ 4.67
                                                      
  Plus sales charge of 5.175% of                      RECORD DATE:  The ninth day of each month
    Public Offering Price (5.457%                     
    of net amount invested in                         DISTRIBUTION DATE:  The fifteenth
    Securities)                             53.03       day of each month
                                                      
  Public Offering Price per Unit         1,024.89     MINIMUM PRINCIPAL DISTRIBUTION:  No
    Plus undistributed net                              distribution need be made from the
    investment income and                               Principal Account if balance therein
    accrued interest                        17.20<F1>   is less than $1 per Unit outstanding
                                                      
    Adjusted Public Offering Price  $    1,042.09     TRUSTEE'S ANNUAL FEE AND EXPENSES
                                                        (including estimated expenses and
                                                        Evaluator's fee) $1.93 per $1,000
SPONSOR'S REPURCHASE PRICE AND                          face amount of underlying Securities    $ 1.93
  REDEMPTION PRICE PER UNIT                           
  (based on bid side evaluation of                    SPONSOR'S ANNUAL PORTFOLIO SUPERVISION
  underlying Securities, $53.03                         FEE:  Maximum of $.25 per $1,000
  less than Adjusted Public                             face amount of underlying Securities       .25
  Offering Price per Unit)          $      989.06     
                                                      TOTAL ESTIMATED ANNUAL EXPENSES
                                                        PER UNIT                                $ 2.18
CALCULATION OF ESTIMATED NET                          
  ANNUAL INTEREST RATE PER UNIT                       EVALUATOR'S FEE FOR EACH EVALUATION:
  (based on face amount of $1,000                       $.40 per issue of Security.
  per Unit)                                           
                                                      
  Annual interest rate per Unit             5.824%    EVALUATION TIME:  4:00 P.M. New York Time
                                                      
  Less estimated annual expenses per                  MANDATORY TERMINATION DATE:  January 1, 2042
    Unit ($2.18) expressed as a                       
    percentage                               .218%    DISCRETIONARY LIQUIDATION AMOUNT:  The Trust
                                                        may be terminated by the Sponsor if
Estimated net annual interest rate                      the value of the portfolio of the Trust at 
  per Unit                                  5.606%      any time is less than $1,522,000.

                

   <F1> Figure shown includes interest accrued (net of expenses) on the underlying Securities to the expected 
date of settlement (normally three business days after purchase) for Units purchased on April 30, 1997.

   <F2> The estimated current return and estimated long term return are increased for transactions entitled to a 
reduced sales charge.  (See "The Units - Estimated Annual Income and Current Return" and "Public Offering of 
Units - Volume Discount" in Part B of this Prospectus.)

                                                A-3
                                                  
                                                  
                                                
</TABLE>


<PAGE>
<TABLE>
<CAPTION>

                                     SUMMARY OF ESSENTIAL INFORMATION
                                                     
                               DEAN WITTER NATIONAL SELECT MUNICIPAL TRUST
                                       DELAWARE PORTFOLIO SERIES 12
                                                     
                                           As of April 30, 1997



<S>                                <C>                <S>                                       <C>

FACE AMOUNT OF SECURITIES           $2,990,000.00     DAILY RATE AT WHICH ESTIMATED NET
                                                        INTEREST ACCRUES PER UNIT               .0147%
                                                      
NUMBER OF UNITS                             3,045     ESTIMATED CURRENT RETURN (based on
                                                        Public Offering Price)<F12>             5.297%
                                                      
FRACTIONAL UNDIVIDED INTEREST IN THE                  ESTIMATED LONG TERM RETURN (based on
  TRUST REPRESENTED BY EACH UNIT        1/3,045th       Public Offering Price)<F12>             5.146%
                                                      
                                                      
PUBLIC OFFERING PRICE                                 MONTHLY INTEREST DISTRIBUTIONS
                                                      
  Aggregate bid side evaluation                         Estimated net annual interest rate
    of Securities in the Trust      $2,914,961.00         per Unit times $1,000                 $52.98
                                                        Divided by 12                           $ 4.41
  Divided by 3,045 Units            $      957.29     
                                                      RECORD DATE:  The ninth day of each month
  Plus sales charge of 4.296% of                      
    Public Offering Price (4.489%                     DISTRIBUTION DATE:  The fifteenth
    of net amount invested in                           day of each month
    Securities)                             42.97     
                                                      MINIMUM PRINCIPAL DISTRIBUTION:  No
  Public Offering Price per Unit         1,000.26       distribution need be made from the
    Plus undistributed principal                        Principal Account if balance therein
    and net investment income and                       is less than $1 per Unit outstanding
    accrued interest                        18.49<F11>    
                                                      TRUSTEE'S ANNUAL FEE AND EXPENSES
    Adjusted Public Offering Price  $    1,018.75       (including estimated expenses and
                                                        Evaluator's fee) $1.98 per $1,000
                                                        face amount of underlying Securities    $ 1.98
SPONSOR'S REPURCHASE PRICE AND                        
  REDEMPTION PRICE PER UNIT                           SPONSOR'S ANNUAL PORTFOLIO SUPERVISION
  (based on bid side evaluation of                      FEE:  Maximum of $.25 per $1,000
  underlying Securities, $42.97 less                    face amount of underlying Securities       .25
  than Adjusted Public Offering Price                 
  per Unit) plus accrued interest   $      975.78     TOTAL ESTIMATED ANNUAL EXPENSES
                                                        PER UNIT                                $ 2.23
CALCULATION OF ESTIMATED NET                          
  ANNUAL INTEREST RATE PER UNIT                       
  (based on face amount of $1,000                     EVALUATOR'S FEE FOR EACH EVALUATION:
  per Unit)                                             $.40 per issue of Security.
                                                      
  Annual interest rate per Unit             5.521%    EVALUATION TIME:  4:00 P.M. New York Time
                                                      
  Less estimated annual expenses per                  MANDATORY TERMINATION DATE:  January 1, 2042
    Unit ($2.23) expressed as a                       
    percentage                               .223%    DISCRETIONARY LIQUIDATION AMOUNT:  The Trust
                                                        may be terminated by the Sponsor if the value
Estimated net annual interest rate                      of the portfolio of the Trust at any time is
  per Unit                                  5.298%      less than $1,218,000.

                

  <F11>Figure shown includes interest accrued (net of expenses) on the underlying Securities to the expected 
date of settlement (normally three business days after purchase) for Units purchased on April 30, 1997.

  <F12>The estimated current return and estimated long term return are increased for transactions entitled to 
a reduced sales charge.  (See "The Units - Estimated Annual Income and Current Return" and "Public Offering 
of Units - Volume Discount" in Part B of this Prospectus.)

                                                A-4
                                                  
                                                  
                                                F-9
</TABLE>

                     A-3
              SUMMARY OF ESSENTIAL INFORMATION
                 (Continued)


 THE TRUSTS -- The Dean Witter Select Municipal Trust,
 National Portfolio Series 126 (the "National Trust") and
 Delaware Portfolio Series 12 (the "Delaware Trust") are two
 separate unit investment trusts (collectively, the "Trusts")
 created on May 6, 1993 (the "Date of Deposit"), under the laws
 of the State of New York pursuant to an Indenture as defined in
 Part B.  Each of the Trusts is composed of "investment grade"
 long-term interest bearing municipal bonds (the "Securities").
 (For a description of the meaning of "investment grade"
 securities, see:  "Bond Ratings", in Part B.)  The objectives
 of each Trust are:  (1) the receipt of income which, under
 existing law, is excludable from gross income for Federal
 income tax purposes (except in certain instances depending on
 the Unit Holders) and, in the case of the Delaware Trust only,
 is exempt from State of Delaware income taxation to individual
 Unit Holders resident in the State of Delaware; and (2) the
 conservation of capital.  The interest income from the Delaware
 Trust, however, may be includable in a Unit Holder's
 alternative minimum taxable income in some cases.  The payment
 of interest and the preservation of principal of the Trusts is
 dependent on the continuing ability of the respective Issuers
 of the Securities thereof to meet their obligations to pay
 principal and interest on the Securities.  Therefore, there is
 no guarantee that the objectives of the Trusts will be
 achieved.  All of the Securities in each of the Portfolios are
 obligations of states or of the counties, municipalities or
 public authorities thereof.  Interest on the Securities, in the
 opinion of bond counsel or special tax counsel to the Issuers
 thereof, under existing law, is excludable from gross income
 for Federal income tax purposes (except in certain instances
 depending on the Unit Holders) and, in the case of the Delaware
 Trust only, is exempt from State of Delaware income taxes when
 owned by individual Unit Holders resident in the State of
 Delaware, except that interest on one Security in the Delaware
 Trust will be a tax preference item for individuals and
 corporations for alternative minimum tax purposes.  (For a
 discussion of certain tax aspects of the Trusts, see:  "Tax
 Status", in Part B.  For a discussion of certain state tax
 aspects of the Delaware Trust, see:  "Special Considerations
 Regarding Delaware Securities -- Delaware Tax Status", herein.)

 OFFERS TO SELL OR THE SOLICITATION OF ORDERS TO BUY
 MAY ONLY BE MADE IN THOSE JURISDICTIONS IN WHICH THE UNITS OF
 EACH TRUST HAVE BEEN REGISTERED.  INVESTORS SHOULD CONTACT
 ACCOUNT EXECUTIVES OF THE SPONSOR TO DETERMINE WHETHER THE
 UNITS OF A PARTICULAR TRUST HAVE BEEN REGISTERED FOR SALE IN
 THE STATE IN WHICH THEY RESIDE.

                     A-4
           MONTHLY DISTRIBUTIONS -- Monthly distributions of
 principal, premium, if any, and interest received by each Trust
 will be made, on or shortly after the fifteenth day of each
 month to Unit Holders of record on the ninth day of such month.
 Alternatively, Unit Holders may elect to have their monthly
 distributions reinvested in either of the Reinvestment Programs
 of the Sponsor.  (See:  "Reinvestment Programs", in Part B).

 PUBLIC OFFERING PRICE -- The Public Offering Price
 per Unit of each Trust is calculated daily, and is equal to the
 aggregate bid side evaluation of the underlying Securities,
 divided by the number of Units outstanding, plus a sales charge
 calculated by reference to "Sales Charge/Volume Discount",
 below, plus the per Unit balance in the Interest and Principal
 Accounts.  Units are offered at the Public Offering Price, plus
 accrued interest.  (See:  "Public Offering of Units", in Part
 B.)

 ESTIMATED CURRENT RETURN -- The Estimated Current
 Return shows the return based on the Public Offering Price and
 is computed by multiplying the estimated net annual interest
 rate per Unit (which shows the return based on a $1,000 face
 amount) by $1,000 and dividing the result by the Public
 Offering Price (not including accrued interest).  The net
 annual interest rate per Unit will vary with changes in the
 fees and expenses of the Trustee, the Sponsor and the Evaluator
 and with the exchange, redemption, sale or maturity of the
 underlying Securities.  In addition, the Public Offering Price
 will also vary with fluctuations in the bid side evaluation of
 the underlying Securities.  Therefore, it can be expected that
 the Estimated Current Return will fluctuate in the future.
 (See:  "The Units -- Estimated Annual Income and Current
 Return", in Part B.)

 MARKET FOR UNITS -- The Sponsor, though not obligated
 to do so, intends to maintain a market for the Units based on
 the aggregate bid side evaluation of the underlying Securities,
 as more fully described in Part B -- "Public Offering of Units
 -- Secondary Market".  If such market is not maintained, a Unit
 Holder will be able to dispose of its Units through redemption
 at prices based on the aggregate bid side evaluation of the
 underlying Securities.  (See:  "Redemption", in Part B.)
 Market conditions may cause such prices to be greater or less
 than the amount paid for Units.

 SPECIAL CONSIDERATIONS -- An investment in Units of
 the Trusts should be made with an understanding of the risks
 which an investment in fixed rate long-term debt obligations
 may entail, including the risk that the value of the Units will
 decline with increases in interest rates.  The National Trust
 is considered to be concentrated in Electric and Power
 Securities (40.51% of the aggregate market value of the
                     A-5   
 National Trust Portfolio).  The Delaware Trust is considered to
 be concentrated in Electric and Power Securities and General
 Obligation Securities (31.86% and 38.18%, respectively, of the
 aggregate market value of the Delaware Trust Portfolio).  (See:
 "The Trust -- Special Considerations" and "The Trust -- Summary
 Description of the Portfolios", in Part B.  See also:  "The
 National Trust" or "The Delaware Trust", herein, for a
 discussion of additional risks relating to Units of such
 Trust.)
    
 OTHER INFORMATION -- The Securities in the Portfolio
 of each Trust were chosen in part on the basis of their
 respective maturity dates.  A long term Trust contains
 obligations maturing in 15 years or more from the Date of
 Deposit.  The maturity date of each Trust is January 1, 2042.
 The latest maturity of a Security in the National Trust is
 January 2031; and the average life to maturity (or date of
 pre-refunding of a bond) of the Portfolio of Securities therein
 is 23.085 years.  The latest maturity of a Security in the
 Delaware Trust is June 2021; and the average life to maturity
 (or date of pre-refunding of a bond) of the Portfolio of
 Securities therein is 17.901 years.  The actual maturity dates
 of each of the Securities contained in each Trust are shown on
 the respective "Schedule of Portfolio Securities", herein.

 The Trustee shall receive annually 75 cents per
 $1,000 principal amount of Securities in each Trust for its
 services as Trustee.  See:  "Expenses and Charges", in Part B,
 for a description of other fees and charges which may be
 incurred by a Trust.

 SALES CHARGE/VOLUME DISCOUNT -- The Public Offering
 Price per Unit will be computed by dividing the aggregate of
 the bid prices of the Securities in a Trust by the number of
 Units outstanding and then adding the appropriate sales charge
 described below.

 The sales charge will reflect different rates
 depending upon the maturities of the various underlying
 Securities.  The sales charge per Unit in the secondary market
 (the "Effective Sales Charge") will be computed by multiplying
 the Evaluator's determination of the bid side evaluation of
 each Security by a sales charge determined in accordance with
 the table set forth below based upon the number of years
 remaining to the maturity of each such Security, totalling all
 such calculations, and dividing this total by the number of
 Units then outstanding.  In calculating the date of maturity, a
 Security will be considered to mature on its stated maturity
 date unless:  (a) the Security has been called for redemption
 or funds or securities have been placed in escrow to redeem it
 on an earlier call date, in which case the call date will be
 deemed the date on which such Security matures; or (b) the
                     A-6
 Security is subject to a mandatory tender, in which case the
 mandatory tender date will be deemed the date on which such
 Security matures.

                       (as % of bid      (as % of Public
 Time to Maturity                side evaluation)  Offering Price)


 Less than one year.................      0%               0%
 1 year to less than 2 years........  0.756%            0.75%
 2 years to less than 4 years.......  1.523%            1.50%
 4 years to less than 7 years.......  2.564%            2.50%
 7 years to less than 11 years......  3.627%            3.50%
 11 years to less than 15 years.....  4.712%            4.50%
 15 years and greater...............  5.820%            5.50%

 The Effective Sales Charge per Unit for a sale in the
 secondary market, as determined above, will be reduced on a
 graduated scale for sales to any single purchaser on a single
 day of the specified number of Units of a Trust set forth
 below.

                                    Dealer Concession
                % of Effective      as % of Effective
 Number of Units            Sales Charge        Sales Charge   


1-99                   100%                    65%
100-249                95%                    62%
250-499                85%                    55%
500-999                70%                    45%
1,000 or more          55%                    35%

 To qualify for the reduced sales charge and
 concession applicable to quantity purchases, the selling dealer
 must confirm that the sale is to a single purchaser, as
 described in "Volume Discount" in Part B of the Prospectus.

 Units purchased at an Effective Sales Charge (before
 volume purchase discount) of less than 3.00% of the Public
 Offering Price (3.093% of the bid side evaluation of the
 Securities) will not be eligible for exchange at a reduced
 sales charge described under the Exchange Option.

 Dealers purchasing certain dollar amounts of Units
 during the life of the Trusts may be entitled to additional
 concessions.  The Sponsor reserves the right, at any time and
 from time to time, to change the level of dealer concessions.

 For further information regarding the volume
 discount, see:  "Public Offering of Units -- Volume Discount",
 in Part B.
                     A-7   
           Note:  "Auditors" in Part B is amended so that
 "Deloitte & Touche" is replaced with "Deloitte & Touche LLP";
 "Evaluator" in Part B is amended so that "Kenny S&P Evaluation
 Services, a division of Kenny Information Systems, Inc." is
 replaced with "Kenny S&P Evaluation Services, a Division of
 J.J. Kenny Co., Inc."; and "Trustee" in Part B is amended so
 that "United States Trust Company of New York, with its
 principal place of business at 114 West 47th Street, New York,
 New York 10036, and its unit investment trust office at 770
 Broadway, New York, New York 10003" is replaced with "The Chase
 Manhattan Bank, a New York Bank with its principal executive
 office located at 270 Park Avenue, New York 10017 and its unit
 investment trust office at 4 New York Plaza, New York, New York
 10004".  The reference to the fifth and five business day in
 "Redemption -- Computation of Redemption Price per Unit" and
 "Administration of the Trust -- Distribution of Interest and
 Principal" in Part B is amended to read third and three,
 respectively.

 On May 31, 1997, Dean Witter, Discover & Co., Dean
 Witter's former parent company, and Morgan Stanley Group Inc.
 merged to form MCDWD.  In connection with such merger, the
 corporate name or DWDC was changed to Morgan Stanley, Dean
 Witter, Discover & Co. ("MCDWD").
    
                     A-8

                       THE NATIONAL TRUST

 The Portfolio of the National Trust consists of
 eleven issues of Securities, ten of which were issued by
 Issuers located in nine states and one of which (approximately
 11.62% of the aggregate market value of the National Trust
 Portfolio) was issued by an Issuer located in the District of
 Columbia.  Two issues of Securities are each a general
 obligation of an Issuer.  Issues of Securities, while not
 backed by the taxing power of the Issuer, are payable from
 revenues or receipts derived from specific projects or other
 available sources.  The National Trust contains the following
 categories of Securities:
   
                          Percentage of Aggregate
                          Market Value of Trust
                                 Portfolio
 Category of Security                   (as of June 6, 1997)


 Electric and Power ................         40.51%
 General Obligation ................         23.43%
 Health Care and Hospital                  19.12%
 Housing ...........................         7.16%
 Water and Sewer ...................         8.63%
 Prerefunded/Escrowed to
   Maturity ........................         1.15%
 Original Issue Discount ...........        66.55 %

 See:  "The Trust -- Summary Description of the
 Portfolios", in Part B, for a summary of the investment risks
 associated with the type of Securities contained in the
 National Trust.  See:  "Tax Status", in Part B, for a
 discussion of certain tax considerations with regard to
 Original Issue Discount.

 Of the Original Issue Discount bonds in the National
 Trust, approximately 5.56% of the aggregate principal amount of
 the Securities in the National Trust (or 1.15% of the market
 value of all Securities in the National Trust on June 6, 1997)
 are zero coupon bonds (including bonds known as multiplier
 bonds, money multiplier bonds, capital accumulator bonds,
 compound interest bonds and discount maturity payment bonds).

 Securities representing approximately 14.48% and
 8.63% of the aggregate market value of the Portfolio are
 subject to redemption at the option of the Issuer thereof
 beginning in 1998 and 1999, respectively.  (See:  "Schedule of
 Portfolio Securities," herein, and "The Trust _ Summary
 description of the Portfolios _ Additional Securities
 considerations _ Redemption of Securities," in Part B.)

                     A-9

           On June 6, 1997, based on the bid side of the market,
 the aggregate market value of the Securities in the National
 Trust was $3,501,945.60.

 On June 6, 1997, Standard & Poor's Corporation rated
 eight of the Securities in the National Trust as follows:
 28.95%-AAA, 27.35%-AA, 13.27%-A and 23.56%-BBB; and Moody's
 Investors Service rated three of the Securities as follows:
 1.15%-Aaa, 5.72%-A, and 11.62%-Ba.  (See:  the respective
 "Schedule of Portfolio Securities", herein, and "Bond Ratings",
 in Part B.)  A Security in the Portfolio may subsequently cease
 to be rated or the rating assigned may be reduced below the
 minimum requirements of the National Trust for the acquisition
 of Securities.  While such events may be considered by the
 Sponsor in determining whether to direct the Trustee to dispose
 of the Security (see:  "Sponsor -- Responsibility", in Part B),
 such events do not automatically require the elimination of
 such Security from the Portfolio.
    
                       THE DELAWARE TRUST

The Portfolio of the Delaware Trust consists of nine issues of Securities, nine 
of which were issued by Issuers located in Delaware.  Three issues of 
Securities are each a general obligation of an Issuer.  Six issues of 
Securities, while not backed by the taxing power of the Issuer, are payable 
from revenues or receipts derived from specific projects or other available 
sources.  The Delaware Trust contains the following categories of Securities:
   
                                      Percentage of Aggregate
                                      Market Value of Trust 
                                           Portfolio
Category of Security		         (as of June 6, 1997)   

Electric and Power 	                 31.86%
General Obligation 	                 38.18%
Highway & Transportation              8.44%
Housing 	                            2.29%
Prerefunded/Escrowed to 
  Maturity 	                      19.23%
Original Issue Discount	            73.07%
Private Activity AMT 	            2.29%
    
      See:  "The Trust -- Summary Description of the Portfolios", in Part B, 
for a summary of the investment risks associated with the type of Securities 
contained in the Delaware Trust.  See:  "Tax Status", in Part B, for a 
discussion of certain tax considerations with regard to Original Issue 
Discount.
   
     Of the Original Issue Discount bonds in the Delaware Trust, approximately 
6.38% of the aggregate principal amount of the Securities in the Delaware Trust 
(or 2.29% of the market value of all Securities in the Delaware Trust on June 
6, 1997) are zero coupon bonds (including bonds known as multiplier bonds, 
money multiplier bonds, capital accumulator bonds, compound interest bonds and 
discount maturity payment bonds).

        Securities representing approximately 9.08% of the aggregate market 
value of the Portfolio are subject to redemption at the option of the Issuer 
thereof beginning in 1999.  (See:  "Schedule of Portfolio Securities," herein, 
and "The Trust - Summary description of the Portfolios - Additional 
Securities considerations - Redemption of Securities," in Part B.)  
    
ALTERNATIVE MINIMUM TAX -- Accrued interest on the zero coupon bond will be a 
tax preference item for alternative minimum tax purposes (see:  Schedule of 
Portfolio Securities).  Although such accrued interest will not be 
distributed to Unit Holders on a current basis, Unit Holders subject to the 
alternative minimum tax will be subject to such tax on such interest as if a 
current distribution of such amounts had been made.
   
          On June 6, 1997, based on the bid side of the market, the aggregate 
market value of the Securities in the Delaware Trust was $2,955,322.80.

           On June 6, 1997, Standard & Poor's Corporation rated eight of the 
Securities in the Delaware Trust as follows:  67.91%-AAA, 17.51%-AA and 
12.29%-A; and Moody's Investors Service rated one of the Securities as 
follows:  2.29%-A.  (See:  the respective "Schedule of Portfolio Securities", 
herein, and "Bond Ratings", in Part B.)  A Security in the Portfolio may 
subsequently cease to be rated or the rating assigned may be reduced below 
the minimum requirements of the Delaware Trust for the acquisition of 
Securities.  While such events may be considered by the Sponsor in determining 
whether to direct the Trustee to dispose of the Security (see:  "Sponsor -- 
Responsibility", in Part B), such events do not automatically require the 
elimination of such Security from the Portfolio.
    
   
              SPECIAL CONSIDERATIONS REGARDING
             DELAWARE SECURITIES - June 12, 1997
    

          The Sponsor believes the information summarized
below describes some of the more significant developments
relating to the general economic conditions of the State of
Delaware and in particular to the State government itself.
This information may be relevant to the Securities (i) of or
supported by the State of Delaware or (ii) of municipalities
or other political subdivisions or instrumentalities of the
State of Delaware that rely, in whole or in part, on ad
valorem real property taxes and other general or special
funds of such municipalities or political subdivisions.  The
sources of such information include publicly available
documents, including the Official Statements of the State.
The Sponsor has not independently verified any of the
information contained in such Official Statements and other
publicly available documents, and is not aware of any facts
that would render such information inaccurate.

Economic Base

   
          The growth experienced in most sectors of
Delaware's economy for the past ten years has been
considerably greater than the average growth rates in the
other forty-nine states.  Population grew by 22% in
Delaware, compared with the national growth of 17% and 5% in
the other states in the region (Maryland, New Jersey, New
York, Pennsylvania).  Delaware's 1996 population exceeded
the 1995 head count by 1.1%, the growth rate for the U.S.
was 0.9%, and the growth in the mideast region was 0.1%.
Similarly, Delaware's employment growth from 1986 through
1996 of 25% exceeded the 20% and 5% growth rates of the
nation and the region, respectively.

          During the same period, unemployment rates
declined from a level higher than the national average, to
one lower than the U.S.  Delaware's April 1997 unemployment
rate of 4.2% was lower than the national rate of 4.9%.  The
April average of the other states in the mideast region was
5.4%.  For 1996, Delaware's unemployment rate averaged 5.2%,
lower than the 5.4% rate for the U.S. and the 5.9% regional
average rate for the same year.
    
          Personal income in the State advanced 92% from
1986 through 1996, compared with 80% for the nation and 72%
in the region.  The 1995 poverty rate in the State was
10.3%, considerably lower than the national rate of 13.8%.
In July 1995 State Policy Reports ranked states by gross
state product per capita.  Delaware ranked second of all the
states, with Alaska as the only state that exceeded
<PAGE>

Delaware.  Delaware exceeded the average state in the value
of per capita production by 46%.

          These indicators of above average economic
performance resulted in part from financial decisions made
by the State in the late 1970's and early 1980's.  They
include (1) reducing the top marginal personal income tax
rate from 19.8% to 7.7% and a further reduction effective
January 1997 that lowered the top rate to 6.9%, (2)
broadening the employment base to reduce the influence of
the manufacturing sector on Delaware's economy (from 25% of
all jobs in 1986 to 16% in 1996), (3) reducing regulations
on business - especially banking through the Financial
Center Development Act of 1981, and (4) following fiscally
conservative taxing policies.  In 1993, further deregulatory
legislation was enacted, which increased competitive options
for telecommunications providers and expanded the powers of
limited liability partnerships in Delaware.
   
          Since the national recession in the early 1990s,
employment has grown steadily in Delaware.  Compared with
one year earlier, Delaware's employment in April 1997 had
increased by 8,900 (2.4%) while the nation's employment grew
by 2.2% and the other states in the region saw an increase
of 1.7%.

          Delaware's manufacturing employment continues to
be negatively impacted by the downsizing and restructuring
of the chemical industry.  In April 1997 there were 23,500
chemical workers in Delaware, 10,100 fewer than in the peak
year of 1990.  When comparing April 1997 with April one year
earlier, Delaware's loss of chemical employment was nearly
3%, the same as the region, compared to a 1% loss in the
nation.  Beginning in the spring of 1997, the General Motors
assembly plant in Northern Delaware serves as an overflow
facility producing the Chevrolet Malibu, a mid-sized sedan,
for two years.  Their current employment is 2,900, with
average wages of $19 per hour.  GM will then use the plant
to build the Saturn Innovate.  They expect to assemble
250,000 cars annually and maintain their current employment
level.

          Chrysler, the owner of the only other auto
assembly plant in the State employs 3,200 workers.  Chrysler
is currently undergoing a $500 million retooling of its
facility.  Later this summer that plant will begin producing
sport a utility truck, called the Dodge Dorango.  By 1988,
the Chrysler plant expects to be producing 109,000 such
vehicles annually.  April 1997 manufacturing employment in
Delaware declined by 5% compared with one year ago.  The
U.S. over the same period and the regional manufacturing
employment were unchanged.
<PAGE>

          The State's per capita personal income of $27,622
in 1996 was 14% higher than the national average, ranking
Delaware fifth in the U.S.  For 1996, Delaware's total
personal income advanced by 6.2%, relative to one year
earlier, compared with 4.5% in the U.S. and 4.2% in the
region.

          In the past ten years (1986-96) there has been a
52% growth in net new business firms established in
Delaware, compared with 22% in the U.S. and 14% in the
region.  In 1996 there were 22,000 firms operating in the
State, a growth rate for the year that was the 5th highest
in the nation, and two and one half times that of the U.S.
and five times that of the region.  The business failure
numbers also paint Delaware as an attractive place to own a
successful company.  In 1995, only 45 Delaware businesses
ceased to operate, the lowest number of failures since 1989.
In 1995, only 22 businesses failed in Delaware for each
10,000 firms in existence, compared with failure rates of 86
and 90 per 10,000 firms for the region and the U.S.,
respectively.

          Franchise tax revenue and fees derived from
companies incorporated in Delaware represent the second
largest source (20%) of State General Fund revenue (the
largest contributor is the personal income tax).  There were
51,300 new incorporations in Delaware in 1996, bringing the
number of domestic corporations using the State as their
legal home to more than 300,000.  New incorporations in
Delaware increased by 7% in 1996, compared with 1995.
Although the State is the legal home of only 5% of the
corporations in the U.S., among those are half the companies
listed on the New York Stock Exchange.  Delaware is the
corporate home of 56% of the companies listed in the
"Fortune 500" in 1997.

          The value of Delaware's construction contracts (as
measured by McGraw-Hill) decreased 10% in 1996 compared with
1995.  This decrease compares with the U.S. increase of 8%.
Delaware's strengths were in the nonresidential building
(office space), nonbuilding (highway) and government
building categories.  For the first four months of 1997,.
the value of Delaware's construction contracts was 21%
higher than the comparable period of 1996.  Advances in
highway and housing contracts accounted for most of the
increase.  Construction employment in April 1997 was nearly
10% higher than one year earlier, compared with 4% growth in
the U.S., and a 5% increase in the region.

          Delaware's new private housing authorizations
decreased by 5% in 1996, compared with 1995.  U.S. and the
region's private housing authorizations were 7% and 9%
higher, respectively, for the same period.  For the first
four months of 1997, Delaware's housing authorizations were
<PAGE>

up by 3%, compared with an 11% growth in the region, and a
2% increase in the nation.  There were 1% more Delaware home
sales in 1996 than in 1995, compared with an 8% increase for
the whole country, and a 2% decline for the region.  The
nominal dollar value of Delaware's housing starts was 6%
higher in 1996 than the previous year, compared with
increases of 8% in the region and 11% nationally.

          Newly leased office space in the greater
Wilmington market increased by 40% in 1996 compared with the
prior year, and was 30% higher than the average of the last
five years.  The vacancy rate for Wilmington's Class "A"
buildings was 15% compared with the national average of 14%
in December 1996.  At the same time, the quoted rental price
for this downtown office space was $20 per square foot,
compared to $25 in the average central business district
nationally.  Operating costs on these properties averaged $7
per square foot at the end of 1996.  These costs were
approximately the same as those nationwide, but considerably
less than in neighboring cities.  MBNA, one of the largest
banks in the State, has recently completed construction of
two office buildings totalling 615,000 square feet and an
adjoining parking garage adjacent to the central square in
the City of Wilmington.

          The financial services industry continued to
expand in Delaware, employing 46,100 workers in April 1997.
Those workers in financial services held 3,400 more jobs
than one year earlier, a year-over-year growth rate of 8%,
in spite of the ongoing bank consolidations.  The number of
national finance-related jobs grew by 3% and the number in
the region increased by 1%.  In 1995, Delaware banks had the
third highest return on average assets in the nation, 2.39%
compared with the U.S. average of 1.16%.  Financial
institutions currently number fifty-seven, including twenty
major credit card companies.  Last year, the Delaware credit
card institutions were responsible for issuing 40% of all
credit card debt issued in the U.S.  In June 1995, the State
approved limited expansion powers for out-of-state banks
that want to establish operations in Delaware.

          The Port of Wilmington handled 4.6 million tons of
waterborne cargo in 1996, an increase of 21% compared with
the prior year.  For the first nine months of fiscal 1997,
gross Port revenue of $13.7 million was 11% higher than in
the first nine months of fiscal 1996.  The composition of
the imports has changed since last year, with increases in
wet bulk imports and reductions in steel, dry bulk and
refrigerated cargo.  The wet bulk (primarily oil) cargo pays
a monthly fee for port usage, regardless of tonnage, while
payment for the other cargo is based on weight.
Wilmington's Port exports more American-made cars than any
other port in the U.S.  New Port contracts include
substantial imports of Chilean fruit, Australian beef and

<PAGE>

Volkswagen cars.  In 1996 the Port of Wilmington led all the
Delaware River ports and terminals with 376 ship calls,
according to the Delaware River and Bay Maritime Exchange.
In June 1995 the State agreed to purchase the Port for $40
million, payable over 30 years.  The state also agreed to
invest $30 million in capital improvements in the Port over
the next two years and to assume $66 million of Port debt.
The State assumed the full operating responsibility for the
Port in September 1996.
State Finances

          Fiscal 1996. General Fund expenditures were $1,651
million, an increase of 7% over the previous year, with the
growth primarily for mandated caseload and inflation
adjustments in social service programs.  One significant
feature in the 1996 budget was an initiative to move welfare
recipients into the labor market.  The fiscal 1996 revenue
was $1,656 million, an increase of 3%.  After adjusting for
the phased-in personal income tax cut, the growth of General
Fund revenue was 5% over the prior year.  The fiscal 1996
cumulative cash balance was $379 million, 24% of the
operating budget.  Nationally, cash balances as a percent of
operating spending averaged 6%, according to the National
Association of State Budget Officers.  The State's Budget
Reserve Fund (see "Fiscal Controls" below) remained fully
funded at the 5% level and held balances of $87 million.

          Delaware finances transportation projects
primarily through the Transportation Trust Fund, created in
1987 and funded by dedicated revenue sources including the
motor fuel tax, Turnpike tolls and concessions, motor
vehicle document and registration fees, miscellaneous
transportation related revenue (titling fees, operator
license fees, etc.), and investment earnings on Trust Fund
balances.  Transportation operating expenses and debt
service were $162 million for fiscal 1996, a 1% increase
over the previous year.  The capital program spent another
$124 million.  The State enacted increases in motor vehicle
gasoline and diesel taxes, vehicle document fees, and tolls
on Interstate 95 to replace some of the anticipated bond-
financed capital spending.  These "user fees" for
transportation purposes are expected to provide $178 million
of capital for transportation projects through 1999, and
became effective September 1993.

          In 1993, the U.S. Supreme Court ruled in favor of
Delaware in a case involving intangible abandoned property,
stating that Delaware is entitled to receive abandoned
property held by brokers incorporated in the State.  In
1994, Delaware negotiated a settlement with New York which
allows Delaware to draw down the $220 million windfall
during the next four years.  The fiscal 1996 budget
<PAGE>

authorized the use of these funds (named the Twenty-first
Century Fund) to create public/private partnerships to
enhance the competitiveness of the State.  Specifically
allocated in fiscal 1996 were $35 million for agricultural
land preservation and a parks' maintenance endowment, $42
million for educational technology investments and economic
development projects and $33 million for housing, community
development, and sewer/water projects.

          Fiscal 1997.  The Delaware Economic and Financial
Advisory Council ("DEFAC"), composed of 33 private and
public-sector members appointed by the Governor, provides
revenue and expenditure forecasts for the General Assembly
and the Governor a minimum of six times each year.  The most
recent DEFAC forecast (May 1997) called for General Fund
revenue of $1,777 million for fiscal 1997, a growth of 8%
over the fiscal 1996 revenue.  (Adjusted for the decrease in
personal income tax rates, the growth estimate was 8%.)
Fiscal 1997 expenditures are expected to be $1,768, an
increase of 7% compared with fiscal 1996. Operating
expenditures and debt service from the Transportation Trust
Fund are expected to be $161 million, approximately the same
as the previous year.  The capital spending budgets include
$180 million for transportation projects and $328 million
for other capital improvements supported by the General Fund
and the Twenty-first Century Fund.

          Fiscal 1998.  The May 1997 DEFAC estimate for
revenue in the General Fund was $1,866 million (+5%) and
$244 million in the Transportation Trust Fund, a nearly 4%
increase over the previous year.  A budget for fiscal 1998
is currently under consideration, and is expected to pass by
June 30, 1997.
    
          Fiscal Controls.  A constitutional limit requires
a three-fifths vote of each house of the General Assembly to
pass or increase any tax or license fee.  Appropriation of
more than 98% of estimated General Fund revenue plus
unencumbered General Fund balances from the previous fiscal
year also requires a three-fifths vote of both houses.

          Excess unencumbered General Fund revenue at the
end of a fiscal year must be placed in a Budget Reserve
Account, until that Account accumulates to 5% of estimated
General Fund revenue, according to the State Constitution.
That Account provides a cushion against unanticipated
revenue shortfalls and funds for tax reductions.  The Budget
Reserve Account currently holds $87 million and is fully
funded.
<PAGE>

          Until 1991 the authorization of additional General
Fund debt was restricted to 75% of the principal retirement
of general obligation debt in the prior fiscal year plus any
deauthorized debt in the same year.  Legislation effective
in July 1991 replaced that debt limitation.  The revised
limitations are three:  (a) annual tax supported debt
authorizations cannot exceed 5% of estimated General Fund
revenue, (b) debt service payments of all tax supported debt
(including the Transportation Authority, certificates of
participation and long-term leases) will be limited to 15%
of General Fund plus Transportation Trust Fund revenue, and
(c) General Obligation debt service payments will be limited
to the projected cumulative cash balance for the same fiscal
year.  These debt limits supported the reduction of per
capita General Obligation debt from $784 in fiscal 1987 to
an estimated $734 in fiscal 1997.
<AUDIT-REPORT>

                        INDEPENDENT AUDITORS' REPORT

THE UNIT HOLDERS, SPONSOR AND TRUSTEE
DEAN WITTER SELECT MUNICIPAL TRUST
NATIONAL PORTFOLIO SERIES 126
DELAWARE PORTFOLIO SERIES 12


We have audited the statements of financial condition and schedules of 
portfolio securities of the Dean Witter Select Municipal Trust National 
Portfolio Series 126 and Delaware Portfolio Series 12 as of April 30, 1997, 
and the related statements of operations and changes in net assets for each 
of the three years in the period then ended.  These financial statements are 
the responsibility of the Trustee (see Footnote (a)(1)).  Our responsibility 
is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing 
standards.  Those standards require that we plan and perform the audit to 
obtain reasonable assurance about whether the financial statements are free 
of material misstatement.  An audit includes examining, on a test basis, 
evidence supporting the amounts and disclosures in the financial statements.  
Our procedures included confirmation of the securities owned as of April 30, 
1997 as shown in the statements of financial condition and schedules of 
portfolio securities by correspondence with The Chase Manhattan Bank, the 
Trustee.  An audit also includes assessing the accounting principles used 
and the significant estimates made by the Trustee, as well as evaluating the 
overall financial statement presentation.  We believe that our audits 
provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, 
in all material respects, the financial position of the Dean Witter Select 
Municipal Trust National Portfolio Series 126 and Delaware Portfolio Series 
12 as of April 30, 1997, and the results of their operations and the changes 
in their net assets for each of the three years in the period then ended in 
conformity with generally accepted accounting principles.






DELOITTE & TOUCHE LLP





June 2, 1997
New York, New York








                                    F-1
</AUDIT-REPORT>




<PAGE>
                       STATEMENT OF FINANCIAL CONDITION
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                        NATIONAL PORTFOLIO SERIES 126
                                       
                                April 30, 1997


                                TRUST PROPERTY

Investments in municipal bonds at market value (amortized
  cost $3,695,151) (Note (a) and Schedule of Portfolio
  Securities Notes (4) and (5))                                   $3,690,150

Accrued interest receivable                                           74,173

Cash                                                                   2,187

           Total                                                   3,766,510


                          LIABILITIES AND NET ASSETS

Less Liabilities:

   Accrued Trustee's fees and expenses                                10,872

   Accrued Sponsor's fees                                              1,952

           Total liabilities                                          12,824


Net Assets:

   Balance applicable to 3,797 Units of fractional
     undivided interest outstanding (Note (c)):

      Capital, less net unrealized market
        depreciation of $5,001                       $3,690,150

      Undistributed principal and net investment
        income (Note (b))                                63,536


           Net assets                                             $3,753,686

Net asset value per Unit ($3,753,686 divided by 3,797 Units)      $   988.59




                      See notes to financial statements
                                       






                                     F-2


<PAGE>
                                       
                           STATEMENT OF OPERATIONS
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                        NATIONAL PORTFOLIO SERIES 126



                                               For the years ended April 30,
                                                1997       1996       1995


Investment income - interest                  $223,617   $223,461   $223,315

Less Expenses:

   Trustee's fees and expenses                   7,344      7,344      7,342

   Sponsor's fees                                  951        951        951

           Total expenses                        8,295      8,295      8,293

           Investment income - net             215,322    215,166    215,022

Unrealized market appreciation                  81,285     96,902     12,034

Net increase in net assets resulting from 
  operations                                  $296,607   $312,068   $227,056




                      See notes to financial statements


























                                     F-3


<PAGE>
                      STATEMENT OF CHANGES IN NET ASSETS
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                        NATIONAL PORTFOLIO SERIES 126



                                            For the years ended April 30,
                                           1997         1996         1995

Operations:

   Investment income - net              $  215,322   $  215,166   $  215,022

   Unrealized market appreciation           81,285       96,902       12,034

           Net increase in net assets 
             resulting from operations     296,607      312,068      227,056


Less Distributions to Unit Holders:

   Investment income - net                (212,784)    (212,742)    (212,776)

           Total distributions            (212,784)    (212,742)    (212,776)


Less Capital Share Transactions:

   Redemption of 8 Units                      -          (7,619)        -   

   Accrued interest on redemption             -            (166)        -   

           Total capital share
             transactions                     -          (7,785)        -   

Net increase in net assets                  83,823       91,541       14,280

Net assets:

   Beginning of year                     3,669,863    3,578,322    3,564,042

   End of year (including undistributed
     principal and net investment income 
     of $63,536, and undistributed net
     investment income of $63,479 and 
     $71,167, respectively)             $3,753,686   $3,669,863   $3,578,322




                      See notes to financial statements







                                     F-4


<PAGE>
                       NOTES TO FINANCIAL STATEMENTS
                                      
                     DEAN WITTER SELECT MUNICIPAL TRUST
                       NATIONAL PORTFOLIO SERIES 126
                                      
                               April 30, 1997



(a) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

    The Trust is registered under the Investment Company Act of 1940 as a 
Unit Investment Trust.  The following is a summary of the significant 
accounting policies of the Trust:

(1) Basis of Presentation

    The Trustee has custody of and responsibility for all accounting  
and financial books, records, financial statements and related data  
of the Trust and is responsible for establishing and maintaining a 
system of internal controls directly related to, and designed to 
provide reasonable assurance as to the integrity and reliability 
of, financial reporting of the Trust.  The Trustee is also 
responsible for all estimates and accruals reflected in the Trust's 
financial statements.  The Evaluator determines the price for each 
underlying Security included in the Trust's Portfolio of Securities 
on the basis set forth in Part B of this Prospectus, "Public 
Offering of Units - Public Offering Price".  Under the Securities 
Act of 1933 ("the Act"), as amended, the Sponsor is deemed to be an 
issuer of the Trust Units.  As such, the Sponsor has the 
responsibility of an issuer under the Act with respect to financial 
statements of the Trust included in the Trust's Registration 
Statement under the Act and amendments thereto.

(2) Investments

    Investments are stated at market value as determined by the 
Evaluator based on the bid side evaluations on the last day of 
trading during the period, except that value on the date of deposit 
(May 6, 1993) represents the cost of investments to the Trust based 
on the offering side evaluations as of the day prior to the date of 
deposit.

(3) Income Taxes

    The Trust is not an association taxable as a corporation for 
Federal income tax purposes; accordingly, no provision is required  
for such taxes.

(4) Expenses

    The Trust pays annual Trustee's fees, estimated expenses, 
Evaluator's fees, and annual Sponsor's portfolio supervision fees 
and may incur additional charges as explained under "Expenses and 
Charges - Fees" and "- Other Charges" in Part B of this Prospectus.

(b) DISTRIBUTIONS

    Interest received by the Trust is distributed to the Unit Holders on or 
shortly after the fifteenth day of each month after deducting applicable 
expenses.  Receipts other than interest are distributed as explained in 
"Administration of the Trust - Distribution of Interest and Principal" 
in Part B of this Prospectus.
                                    F-5


<PAGE>
                       NOTES TO FINANCIAL STATEMENTS
                                      
                     DEAN WITTER SELECT MUNICIPAL TRUST
                       NATIONAL PORTFOLIO SERIES 126
                                      
                               April 30, 1997



(c) ORIGINAL COST TO INVESTORS

    The original cost to investors represents the aggregate initial public 
offering price as of the date of deposit (May 6, 1993) exclusive of 
accrued interest, computed on the basis set forth under "Public Offering 
of Units - Public Offering Price" in Part B of this Prospectus.

    A reconciliation of the original cost of Units to investors to the net 
amount applicable to investors as of April 30, 1997  follows:

       Original cost to investors                                $3,876,039
       Less:  Gross underwriting commissions (sales charge)        (189,920)
       Net cost to investors                                      3,686,119
       Net unrealized market depreciation                            (5,001)
       Accumulated interest accretion                                 9,032
       Net amount applicable to investors                        $3,690,150

(d) OTHER INFORMATION

    Selected data for a Unit of the Trust during each year:

                                               For the years ended April 30,
                                               1997        1996        1995
       
       Net investment income distributions 
         during year                         $ 56.04     $ 55.98     $ 55.92
       
       Net asset value at end of year        $988.59     $966.52     $940.43
       
       Trust Units outstanding at end of 
         year                                  3,797       3,797       3,805
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
                                        F-6


<PAGE>
<TABLE>
<CAPTION>
                                   SCHEDULE OF PORTFOLIO SECURITIES
                                                   
                                  DEAN WITTER SELECT MUNICIPAL TRUST
                                    NATIONAL PORTFOLIO SERIES 126
                                                   
                                            April 30, 1997
                                                   
                                                   
                                                   
Port-                                                                                                 Optional
folio                                Rating    Face          Coupon     Maturity  Sinking Fund        Refunding        Market
 No.   Title of Securities            <F3>     Amount         Rate        Date   Redemptions<F5>   Redemptions<F4> Value<F6><F7>

<S> <C>                                <C>     <C>            <C>       <C>          <C>              <C>                <C>
  1. Eutaw Industrial Develop-
     ment Board, Alabama 6.05%
     Pollution Control Revenue
     Refunding Bonds, Series B
     (Alabama Power Company,
     Greene County Plant Proj-
     ect) (MBIA Insured) <F10>           AAA     $  500,000     6.050%    05/01/23     NONE             05/01/98@102    $  503,260

  2. Salt River Project Agri-
     cultural Improvement and
     Power District, Arizona,
     Salt River Project Electric
     System Revenue Bonds, 1991
     Series A                            AA         400,000     6.000     01/01/31     01/01/23@100     01/01/01@100       401,916

  3. Connecticut Housing 
     Finance Authority Housing
     Mortgage Finance Program
     Bonds, 1992 Subseries A-1
     <F9>                                AA         250,000     5.900     11/15/25     11/15/24@100     11/15/02@102       247,945

  4. District of Columbia 
     (Washington, D.C.) General 
     Obligation Refunding Bonds,
     Series 1993A                      Ba<F8>      400,000     6.000     06/01/07     06/01/06@100     NONE               400,276

  5. Washington Wilkes Payroll
     Development Authority,
     Georgia Subordinated Zero
     Coupon Revenue Bonds
     (Southern Care Corporation
     Facility), Series 1991C
     (Escrowed to Maturity)            Aaa<F8>     200,000     0.000     12/01/21     NONE             NONE                38,364

  6. Chicago, Illinois, Water
     Revenue Bonds, Series 1989        AA-         300,000     6.000     11/15/19     11/15/17@100     11/15/99@100       300,759

  7. Indiana Health Facility
     Financing Authority Hospi-
     tal Revenue Bonds, Series
     1993 (Lafayette Home Hos-
     pital Project)                    A1<F8>      200,000     6.000     08/01/23     08/01/14@100     02/01/03@102       195,838

  8. Porter Township High 
     School Building Corporation,
     Indiana First Mortgage
     Bonds, Series 1992                A          400,000     6.000     01/15/15     01/15/13@100     07/15/03@102       408,000

  9. New Jersey Health Care
     Facilities Financing
     Authority Revenue Bonds,
     Pascack Valley Hospital
     Association Issue, Series
     1991                              BBB+       405,000     6.700     07/01/11     07/01/02@100     07/01/01@102       415,392

 10. Allegheny County Hospital
     Development Authority, Penn-
     sylvania, Hospital Revenue
     Bonds, Series Q (Allegheny
     Valley Hospital, Sublessee)       A          250,000     7.000     08/01/15     08/01/14@100     NONE               277,175

 11. Marshall County, West 
     Virginia, Pollution Control
     Revenue Bonds, (Ohio Power
     Company Project), Series D
     (MBIA Insured) <F10>              AAA        500,000     5.900     04/01/22     NONE             04/01/03@102       501,225

                                               $3,805,000                                                             $3,690,150




                                                 See notes to schedule of portfolio securities
                                                                      F-7
</TABLE>


<PAGE>
               NOTES TO SCHEDULE OF PORTFOLIO SECURITIES
                                    
                   DEAN WITTER SELECT MUNICIPAL TRUST
                     NATIONAL PORTFOLIO SERIES 126
                                    
                             April 30, 1997



[FN]

<F3> All ratings are provided by Standard & Poor's Corporation, unless 
otherwise indicated.  A brief description of applicable Security 
ratings is given under "Bond Ratings" in Part B of this Prospectus.

<F4> There is shown under this heading the date on which each issue of 
Securities is redeemable by the operation of optional call 
provisions and the redemption price for that date; unless otherwise 
indicated, each issue continues to be redeemable at declining 
prices thereafter but not below par.  Securities listed as non-
callable, as well as Securities listed as callable, may also be 
redeemable at par under certain circumstances from special 
redemption payments.

<F5> There is shown under this heading the date on which an issue of 
Securities is subject to scheduled sinking fund redemption and the 
redemption price of par.

<F6> The market value of the Securities as of April 30, 1997 was 
determined by the Evaluator on the basis of bid side evaluations 
for the Securities at such date.

<F7> At April 30, 1997, the net unrealized market depreciation of all 
Securities was comprised of the following:

       Gross unrealized market appreciation            $ 14,701
       
       Gross unrealized market depreciation             (19,702)
       
       Net unrealized market depreciation              $ (5,001)

    The amortized cost of the Securities for Federal income tax 
purposes was $3,695,151 at April 30, 1997.

<F8>  Moody's Investors Service Inc. rating.

<F9>  See "The Trust - Summary Description of the Portfolios - Revenue 
Securities - Housing Securities" in Part B of this Prospectus for 
the discussion relating to Housing Securities therein.

<F10> Insured by Municipal Bond Insurance Association ("MBIA").








                                  F-8




<PAGE>
                       STATEMENT OF FINANCIAL CONDITION
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                         DELAWARE PORTFOLIO SERIES 12
                                       
                                April 30, 1997


                                TRUST PROPERTY

Investments in municipal bonds at market value (amortized
  cost $2,965,072) (Note (a) and Schedule of Portfolio
  Securities Notes (4) and (5))                                   $2,914,961

Accrued interest receivable                                           56,710

Cash                                                                   3,049

           Total                                                   2,974,720


                          LIABILITIES AND NET ASSETS

Less Liabilities:

   Accrued Trustee's fees and expenses                                 3,267

   Accrued Sponsor's fees                                              1,542

           Total liabilities                                           4,809


Net Assets:

   Balance applicable to 3,045 Units of fractional
     undivided interest outstanding (Note (c)):

      Capital, less net unrealized market
        depreciation of $50,111                      $2,914,961

      Undistributed principal and net investment
        income (Note (b))                                54,950


           Net assets                                             $2,969,911

Net asset value per Unit ($2,969,911 divided by 3,045 Units)      $   975.34




                      See notes to financial statements







                                     F-10


<PAGE>
                           STATEMENTS OF OPERATIONS
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                         DELAWARE PORTFOLIO SERIES 12



                                               For the years ended April 30,
                                                1997       1996       1995


Investment income - interest                  $173,425   $173,393   $173,242

Less Expenses:

   Trustee's fees and expenses                   5,935      5,967      5,981

   Sponsor's fees                                  749        753        755

           Total expenses                        6,684      6,720      6,736

           Investment income -
             net                               166,741    166,673    166,506

Net gain on investments:

   Realized loss on securities sold or 
     redeemed                                   (1,585)      (371)    (2,091)

   Net unrealized market appreciation           25,585     53,056     36,276

           Net gain on investments              24,000     52,685     34,185

Net increase in net assets resulting from 
  operations                                  $190,741   $219,358   $200,691




                      See notes to financial statements



















                                     F-11


<PAGE>
                     STATEMENTS OF CHANGES IN NET ASSETS
                                       
                      DEAN WITTER SELECT MUNICIPAL TRUST
                         DELAWARE PORTFOLIO SERIES 12



                                            For the years ended April 30,
                                           1997         1996         1995

Operations:

   Investment income - net              $  166,741   $  166,673   $  166,506

   Realized loss on securities sold or 
     redeemed                               (1,585)        (371)      (2,091)

   Net unrealized market appreciation       25,585       53,056       36,276

           Net increase in net assets
             resulting from operations     190,741      219,358      200,691


Less Distributions to Unit Holders:

   Principal                                (6,760)      (3,075)      (7,064)

   Investment income - net                (161,141)    (161,141)    (161,141)

           Total distributions            (167,901)    (164,216)    (168,205)

Increase in net assets                      22,840       55,142       32,486

Net assets:

   Beginning of year                     2,947,071    2,891,929    2,859,443

   End of year (including undistributed 
     principal and net investment in-
     come of $54,950, $54,639 and
     $55,848, respectively)             $2,969,911   $2,947,071   $2,891,929




                      See notes to financial statements













                                     F-12


<PAGE>
                       NOTES TO FINANCIAL STATEMENTS
                                      
                     DEAN WITTER SELECT MUNICIPAL TRUST
                        DELAWARE PORTFOLIO SERIES 12
                                      
                               April 30, 1997



(a) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

    The Trust is registered under the Investment Company Act of 1940 as a 
Unit Investment Trust.  The following is a summary of the significant 
accounting policies of the Trust:

(1) Basis of Presentation

    The Trustee has custody of and responsibility for all accounting
and financial books, records, financial statements and related data 
of the Trust and is responsible for establishing and maintaining a 
system of internal controls directly related to, and designed to 
provide reasonable assurance as to the integrity and reliability 
of, financial reporting of the Trust.  The Trustee is also 
responsible for all estimates and accruals reflected in the Trust's 
financial statements.  The Evaluator determines the price for each 
underlying Security included in the Trust's Portfolio of Securities 
on the basis set forth in Part B of this Prospectus, "Public 
Offering of Units - Public Offering Price".  Under the Securities 
Act of 1933 ("the Act"), as amended, the Sponsor is deemed to be an 
issuer of the Trust Units.  As such, the Sponsor has the 
responsibility of an issuer under the Act with respect to financial 
statements of the Trust included in the Trust's Registration 
Statement under the Act and amendments thereto.

(2) Investments

    Investments are stated at market value as determined by the 
Evaluator based on the bid side evaluations on the last day of 
trading during the period, except that value on the date of deposit 
(May 6, 1993) represents the cost of investments to the Trust based 
on the offering side evaluations as of the day prior to the date of 
deposit.

(3) Income Taxes

    The Trust is not an association taxable as a corporation for 
Federal income tax purposes; accordingly, no provision is required 
for such taxes.

(4) Expenses

    The Trust pays annual Trustee's fees, estimated expenses, 
Evaluator's fees, and annual Sponsor's portfolio supervision fees 
and may incur additional charges as explained under "Expenses and 
Charges - Fees" and "- Other Charges" in Part B of this Prospectus.




                                      F-13


<PAGE>
                       NOTES TO FINANCIAL STATEMENTS
                                      
                     DEAN WITTER SELECT MUNICIPAL TRUST
                        DELAWARE PORTFOLIO SERIES 12
                                      
                               April 30, 1997



(b) DISTRIBUTIONS

    Interest received by the Trust is distributed to the Unit Holders on or 
shortly after the fifteenth day of each month after deducting applicable 
expenses.  Receipts other than interest are distributed as explained in 
"Administration of the Trust - Distribution of Interest and Principal" 
in Part B of this Prospectus.

(c) ORIGINAL COST TO INVESTORS

    The original cost to investors represents the aggregate initial public 
offering price as of the date of deposit (May 6, 1993) exclusive of 
accrued interest, computed on the basis set forth under "Public Offering 
of Units - Public Offering Price" in Part B of this Prospectus.

    A reconciliation of the original cost of Units to investors to the net 
amount applicable to investors as of April 30, 1997 follows:

       Original cost to investors                               $3,118,293
       Less:  Gross underwriting commissions (sales charge)       (152,806)
       Net cost to investors                                     2,965,487
       Cost of securities sold or redeemed                         (21,348)
       Net unrealized market depreciation                          (50,111)
       Accumulated interest accretion                               20,933
       Net amount applicable to investors                       $2,914,961
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
                                        F-14


<PAGE>
                       NOTES TO FINANCIAL STATEMENTS
                                      
                     DEAN WITTER SELECT MUNICIPAL TRUST
                        DELAWARE PORTFOLIO SERIES 12
                                      
                               April 30, 1997



(d) OTHER INFORMATION

    Selected data for a Unit of the Trust during each year:

                                               For the years ended April 30,
                                               1997        1996        1995
       
       Interest income                       $ 56.95     $ 56.94     $ 56.89
       Expenses                                (2.19)      (2.21)      (2.21)
       Investment income - net                 54.76       54.73       54.68
       Income distributions                   (52.92)     (52.92)     (52.92)
                                                1.84        1.81        1.76
       Principal distributions                 (2.22)      (1.01)      (2.32)
       Realized loss on securities
         sold or redeemed                       (.52)       (.12)       (.69)
       Net unrealized market appreciation       8.40       17.43       11.92
       Net increase in net asset value          7.50       18.11       10.67
       Net asset value - beginning of 
         year                                 967.84      949.73      939.06
       Net asset value - end of year         $975.34     $967.84     $949.73
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
                                        F-15


<PAGE>
<TABLE>
<CAPTION>
                                   SCHEDULE OF PORTFOLIO SECURITIES
                                                   
                                  DEAN WITTER SELECT MUNICIPAL TRUST
                                     DELAWARE PORTFOLIO SERIES 12
                                                   
                                            April 30, 1997
                                                   
                                                   
                                                   
Port-                                                                                                 Optional
folio                               Rating       Face     Coupon   Maturity       Sinking Fund        Refunding       Market
 No.   Title of Securities           <F13>      Amount     Rate       Date        Redemptions<F15>  Redemptions<F14> Value<F16><F17>

<S> <C>                              <C>       <C>           <C>       <C>          <C>              <C>              <C>
  1. Delaware Economic Develop-
     ment Authority, 6.75% Pol-
     lution Control Refunding
     Revenue Bonds (Delmarva
     Power & Light Company),
     Series 1992B (AMBAC
     Insured) <F20>                  AAA       $  400,000    6.750%    05/01/19     NONE             05/01/02@102     $  429,528

  2. Delaware State Housing
     Authority, Senior Home
     Mortgage Revenue Bonds,
     1991 Series A <F19><F22>        Aa3<F23>     200,000    0.000     12/01/10     NONE             NONE                 70,352

  3. Delaware Transportation
     Authority Transportation
     System Senior Revenue
     Bonds, 1991 Series
     (Refunded) <F18>                AAA          275,000    6.500     07/01/11     NONE             07/01/01@102        297,619

  4. Delaware Transportation
     Authority Transportation
     System Senior Revenue
     Bonds, 1991 Series              AA           250,000    5.500     07/01/16     07/01/15@100     07/01/01@100        244,762

  5. Dover Electric Revenue
     Refunding Bonds, (Series
     1993) (FGIC Insured) <F21>      AAA          500,000    5.750     07/01/15     07/01/12@100     01/01/03@102        500,260

  6. Georgetown General Obliga-
     tion Bonds, Series of 1993
     (AMBAC Insured) <F20>           AAA          500,000    5.750     06/01/21     06/01/14@100     06/01/03@100        491,655

  7. Sussex County General
     Obligation Refunding Bonds,
     Series 1993                     A+           365,000    5.600     10/15/20     10/15/13@100     04/15/03@102        353,875

  8. University of Delaware 
     Revenue Bonds, Series 1989
     (Refunded) <F18>                AA+          250,000    6.625     11/01/10     NONE             11/01/99@102        266,977

  9. Wilmington Parking Author-
     ity Guaranteed Parking Rev-
     enue Bonds, Series of 1992A
     (FGIC Insured) <F21>            AAA          250,000    6.000     09/15/09     09/15/08@100     09/15/02@102        259,933

                                               $2,990,000                                                             $2,914,961




                                                   See notes to schedule of portfolio securities
                                                                        F-16
</TABLE>


<PAGE>
               NOTES TO SCHEDULE OF PORTFOLIO SECURITIES
                                    
                   DEAN WITTER SELECT MUNICIPAL TRUST
                      DELAWARE PORTFOLIO SERIES 12
                                    
                             April 30, 1997



[FN]

 <13>All ratings are provided by Standard & Poor's Corporation, unless 
otherwise indicated.  A brief description of applicable Security 
ratings is given under "Bond Ratings" in Part B of this Prospectus.

 <F14>There is shown under this heading the date on which each issue of 
Securities is redeemable by the operation of optional call 
provisions and the redemption price for that date; unless otherwise 
indicated, each issue continues to be redeemable at declining 
prices thereafter but not below par.  Securities listed as non-
callable, as well as Securities listed as callable, may also be 
redeemable at par under certain circumstances from special 
redemption payments.

 <F15>There is shown under this heading the date on which an issue of 
Securities is subject to scheduled sinking fund redemption and the 
redemption price on such date.

 <F16>The market value of the Securities as of April 30, 1997 was 
determined by the Evaluator on the basis of bid side evaluations 
for the Securities at such date.

 <F17>At April 30, 1997, the net unrealized market depreciation of all 
Securities was comprised of the following:

       Gross unrealized market appreciation         $  6,949
       
       Gross unrealized market depreciation          (57,060)
       
       Net unrealized market depreciation           $(50,111)

    The amortized cost of the Securities for Federal income tax 
purposes was $2,965,072 at April 30, 1997.

 <F18>The Issuer has indicated that it will refund this Security on its 
optional redemption date.

 <19>In the opinion of bond counsel to the issuing government authority, 
interest on this bond will be a tax preference item for individuals 
and corporations for alternative minimum tax purposes (see "Tax 
Status" herein).

 <F20>Insured by American Municipal Bond Assurance Corporation ("AMBAC").

 <F21>Insured by Financial Guaranty Insurance Company ("FGIC").

 <F22>See "The Trust - Summary Description of the Portfolios - Revenue 
Securities - Housing Securities" in Part B of this Prospectus for 
the discussion relating to Housing Securities, therein.

 <F23>Moody's Investors Service, Inc. rating.
                                  F-17




(MODULE)
     (NAME)     DWSMTPARTB941
     (CIK) 0000840581
     (CCC) uit*59fl
 (/MODULE)

           CONTENTS OF REGISTRATION STATEMENT


      This registration statement comprises the following
      documents:

      The facing sheet.

      The Cross Reference Sheet.

      The Prospectus.

      The signatures.

      Consents of the Evaluator and Independent Auditors; all
      other consents were previously filed.

      The following exhibits:

      23. 1a.   Consents of Kenny S&P Evaluation Services, a
      division of J.J. Kenny Co., Inc.

1b.   Consent of Independent Auditors.

      27. 1.    Financial Data Schedule of Dean Witter Select
      Municipal Trust, National Portfolio Series 126.

         2.     Financial Data Schedule of Dean Witter Select
      Municipal Trust, Delaware Portfolio Series 12.



            FINANCIAL STATEMENTS



 1.   Statement of Financial Condition, Statement of Operations
      and Statement of Changes in Net Assets of each Trust, as
      shown in the Prospectus.

                      CONSENT OF COUNSEL


        The consents of counsel to the use of their names in the
Prospectus included in this Registration Statement are contained
in their opinions filed as Exhibits EX-5 and EX-8 to this
Registration Statement.

                          SIGNATURES

   
        Pursuant to the requirements of the Securities Act of
1933, each of the registrants, Dean Witter Select Municipal Trust,
National Portfolio Series 126 and Delaware Portfolio Series 12,
certifies that it meets all of the requirements for effectiveness
of this Registration Statement pursuant to Rule 485(b) under the
Securities Act of 1933 and has duly caused this Post-Effective
Amendment No. 4 to the Registration Statement to be signed on
their behalf by the undersigned, thereunto duly authorized, all in
The City of New York and State of New York on the 26th day of
June, 1997.


                       DEAN WITTER SELECT MUNICIPAL
                         TRUST,
                       NATIONAL PORTFOLIO SERIES 126
                       DELAWARE PORTFOLIO SERIES 12
                         (Registrants)


                       By:  DEAN WITTER REYNOLDS INC.
                                  (Depositor)



                               Thomas Hines          
                               Thomas Hines
                               Authorized Signatory


        Pursuant to the requirements of the Securities Act of
1933, this Post-Effective Amendment No. 4 to the Registration
Statement has been signed on behalf of Dean Witter Reynolds Inc.,
the Depositor, by the following person in the following capacities
and by the following persons who constitute a majority of the
Depositor's Board of Directors in The City of New York and State
of New York on this 26th day of June, 1997.


Name                             Office



Philip J. Purcell                Chairman & Chief Executive
                                 Officer and Director
Richard M. DeMartini             Director
Robert J. Dwyer                  Director
Christine A. Edwards             Director
Charles A. Fiumefreddo           Director
James F. Higgins                 Director
Mitchell M. Merin                Director
Stephen R. Miller                Director
Richard F. Powers III            Director
Thomas C. Schneider              Director
William B. Smith                 Director

                                      Thomas Hines
                                      Thomas Hines
                                 Attorney-in-fact1



             
1    Executed copies of the Powers of Attorney of the Board
   Members listed below have been filed with the Securities and
   Exchange Commission in connection with Amendment No. 1 to the
   Registration Statement on Form S-6 for Dean Witter Select
   Equity, Select 10 Industrial Portfolio 97-1, File No. 333-
   16839, Amendment No. 1 to the Registration Statement on Form
   S-6 for Dean Witter Select Equity Trust, Select 10 Industrial
   Portfolio 96-4, File No. 333-10499 and the Registration
   Statement on Form S-6 for Dean Witter Select Equity Trust,
   Select 10 International Series 95-1, File No. 33-56389.
    


<PAGE>

                        EXHIBIT INDEX


EXHIBIT NO.    TITLE OF DOCUMENT



 23. 1a.     Consents of Kenny S&P Evaluation Services, a
   division of J.J. Kenny Co., Inc.

    1b.           Consent of Deloitte & Touche LLP

 27. 1.      Financial Data Schedule of Dean Witter Select
   Municipal Trust, National Portfolio Series 126.

     2.      Financial Data Schedule of Dean Witter Select
   Municipal Trust, Delaware Portfolio Series 12.

<PAGE>


<PAGE>

         Letterhead of KENNY S&P EVALUATION SERVICES
    A division of J.J. Kenny Co., Inc.


                                         June 26, 1997

Dean Witter Reynolds Inc.
Two World Trade Center
New York, NY  10048

        Re:  Dean Witter Select Municipal Trust,
   National Portfolio Series 126      



Gentlemen:

        We have examined the post-effective Amendment to the
Registration Statement File No. 33-49221 for the above-captioned
trust.  We hereby acknowledge that Kenny S&P Evaluation Services,
a division of J.J. Kenny Co., Inc. is currently acting as the
evaluator for the trust.  We hereby consent to the use in the
Registration Statement of the references to Kenny S&P Evaluation
Services, a division of J.J. Kenny Co., Inc. as evaluator.

        In addition, we hereby confirm that the ratings
indicated in the Registration Statement for the respective bonds
comprising the trust portfolio are the ratings indicated in our
KENNYBASE database as of the evaluation report.

        You are hereby authorized to file a copy of this letter
with the Securities and Exchange Commission.

                       Sincerely,

                       Frank A. Ciccotto
                       Frank A. Ciccotto
                       Vice President

<PAGE>

                                                         Exhibit 23.1b.











                      CONSENT OF INDEPENDENT AUDITORS

We consent to the use of our report dated June 2, 1997, accompanying the
financial statements of the Dean Witter Select Municipal Trust National 
Portfolio Series 126 and Delaware Portfolio Series 12 included herein and to 
the reference to our Firm as experts under the heading "Auditors" in the 
prospectus which is a part of this registration statement.





DELOITTE & TOUCHE LLP







June 26, 1997
New York, New York








<TABLE> <S> <C>

<PAGE>

<ARTICLE>                    6

<LEGEND>                     THE SCHEDULE CONTAINS SUMMARY FINANCIAL
                             INFORMATION EXTRACTED FROM THE FINANCIAL
                             STATEMENTS FOR DEAN WITTER SELECT
                             MUNICIPAL TRUST NATIONAL PORTFOLIO
                             SERIES 126 AND IS QUALIFIED IN ITS
                             ENTIRETY BY REFERENCE TO SUCH FINANCIAL
                             STATEMENTS

<RESTATED>                   

<CIK>                        0000894415

<NAME>                       DEAN WITTER SELECT MUNICIPAL TRUST     
                             NATIONAL PORTFOLIO SERIES 126

<SERIES>                     

<NAME>                       DEAN WITTER SELECT MUNICIPAL TRUST     
                             NATIONAL PORTFOLIO SERIES 

<NUMBER>                     126

<MULTIPLIER>                 1

<FISCAL-YEAR-END>            Apr-30-1997

<PERIOD-START>               May-1-1996

<PERIOD-END>                 Apr-30-1997

<PERIOD-TYPE>                YEAR

<INVESTMENTS-AT-COST>        3,695,151 

<INVESTMENTS-AT-VALUE>       3,690,150 

<RECEIVABLES>                74,173 

<ASSETS-OTHER>               2,187 

<OTHER-ITEMS-ASSETS>         0 

<TOTAL-ASSETS>               3,766,510 

<PAYABLE-FOR-SECURITIES>     0 

<SENIOR-LONG-TERM-DEBT>      0 

<OTHER-ITEMS-LIABILITIES>    12,824 

<TOTAL-LIABILITIES>          12,824 

<SENIOR-EQUITY>              0 

<PAID-IN-CAPITAL-COMMON>     3,687,532 

<SHARES-COMMON-STOCK>        3,797 

<SHARES-COMMON-PRIOR>        3,797 

<ACCUMULATED-NII-CURRENT>    71,155 

<OVERDISTRIBUTION-NII>       0 

<ACCUMULATED-NET-GAINS>      0 

<OVERDISTRIBUTION-GAINS>     0 

<ACCUM-APPREC-OR-DEPREC>     (5,001)

<NET-ASSETS>                 3,753,686 

<DIVIDEND-INCOME>            0 

<INTEREST-INCOME>            221,135 

<OTHER-INCOME>               2,482 

<EXPENSES-NET>               8,295 

<NET-INVESTMENT-INCOME>      215,322 

<REALIZED-GAINS-CURRENT>     0 

<APPREC-INCREASE-CURRENT>    81,285 

<NET-CHANGE-FROM-OPS>        296,607 

<EQUALIZATION>               0 

<DISTRIBUTIONS-OF-INCOME>    212,784 

<DISTRIBUTIONS-OF-GAINS>     0 

<DISTRIBUTIONS-OTHER>        0 

<NUMBER-OF-SHARES-SOLD>      0 

<NUMBER-OF-SHARES-REDEEMED>  0 

<SHARES-REINVESTED>          0 

<NET-CHANGE-IN-ASSETS>       83,823 

<ACCUMULATED-NII-PRIOR>      71,098 

<ACCUMULATED-GAINS-PRIOR>    0 

<OVERDISTRIB-NII-PRIOR>      0 

<OVERDIST-NET-GAINS-PRIOR>   0 

<GROSS-ADVISORY-FEES>        0 

<INTEREST-EXPENSE>           0 

<GROSS-EXPENSE>              0 

<AVERAGE-NET-ASSETS>         0 

<PER-SHARE-NAV-BEGIN>        0 

<PER-SHARE-NII>              0 

<PER-SHARE-GAIN-APPREC>      0 

<PER-SHARE-DIVIDEND>         0 

<PER-SHARE-DISTRIBUTIONS>    0 

<RETURNS-OF-CAPITAL>         0 

<PER-SHARE-NAV-END>          0 

<EXPENSE-RATIO>              0 

<AVG-DEBT-OUTSTANDING>       0 

<AVG-DEBT-PER-SHARE>         0 



</TABLE>

<TABLE> <S> <C>


<PAGE>

<ARTICLE>                    6

<LEGEND>                     THE SCHEDULE CONTAINS SUMMARY FINANCIAL
                             INFORMATION EXTRACTED FROM THE FINANCIAL
                             STATEMENTS FOR DEAN WITTER SELECT
                             MUNICIPAL TRUST DELAWARE PORTFOLIO
                             SERIES 12 AND IS QUALIFIED IN ITS
                             ENTIRETY BY REFERENCE TO SUCH FINANCIAL
                             STATEMENTS

<RESTATED>                   

<CIK>                        0000885389

<NAME>                       DEAN WITTER SELECT MUNICIPAL TRUST     
                             DELAWARE PORTFOLIO SERIES 12

<SERIES>                     

<NAME>                       DEAN WITTER SELECT MUNICIPAL TRUST     
                             DELAWARE PORTFOLIO SERIES
                             
<NUMBER>                     12


<MULTIPLIER>                 1

<FISCAL-YEAR-END>            Apr-30-1997

<PERIOD-START>               May-1-1996

<PERIOD-END>                 Apr-30-1997

<PERIOD-TYPE>                YEAR

<INVESTMENTS-AT-COST>        2,965,072 

<INVESTMENTS-AT-VALUE>       2,914,961 

<RECEIVABLES>                56,710 

<ASSETS-OTHER>               3,049 

<OTHER-ITEMS-ASSETS>         0 

<TOTAL-ASSETS>               2,974,720 

<PAYABLE-FOR-SECURITIES>     0 

<SENIOR-LONG-TERM-DEBT>      0 

<OTHER-ITEMS-LIABILITIES>    4,809 

<TOTAL-LIABILITIES>          4,809 

<SENIOR-EQUITY>              0 

<PAID-IN-CAPITAL-COMMON>     2,965,098 

<SHARES-COMMON-STOCK>        3,045 

<SHARES-COMMON-PRIOR>        3,045 

<ACCUMULATED-NII-CURRENT>    54,924 

<OVERDISTRIBUTION-NII>       0 

<ACCUMULATED-NET-GAINS>      0 

<OVERDISTRIBUTION-GAINS>     0 

<ACCUM-APPREC-OR-DEPREC>     (50,111)

<NET-ASSETS>                 2,969,911 

<DIVIDEND-INCOME>            0 

<INTEREST-INCOME>            168,128 

<OTHER-INCOME>               5,297 

<EXPENSES-NET>               6,684 

<NET-INVESTMENT-INCOME>      166,741 

<REALIZED-GAINS-CURRENT>     (1,585)

<APPREC-INCREASE-CURRENT>    25,585 

<NET-CHANGE-FROM-OPS>        190,741 

<EQUALIZATION>               0 

<DISTRIBUTIONS-OF-INCOME>    161,141 

<DISTRIBUTIONS-OF-GAINS>     0 

<DISTRIBUTIONS-OTHER>        6,760 

<NUMBER-OF-SHARES-SOLD>      0 

<NUMBER-OF-SHARES-REDEEMED>  0 

<SHARES-REINVESTED>          0 

<NET-CHANGE-IN-ASSETS>       22,840 

<ACCUMULATED-NII-PRIOR>      54,623 

<ACCUMULATED-GAINS-PRIOR>    0 

<OVERDISTRIB-NII-PRIOR>      0 

<OVERDIST-NET-GAINS-PRIOR>   0 

<GROSS-ADVISORY-FEES>        0 

<INTEREST-EXPENSE>           0 

<GROSS-EXPENSE>              0 

<AVERAGE-NET-ASSETS>         0 

<PER-SHARE-NAV-BEGIN>        0 

<PER-SHARE-NII>              0 

<PER-SHARE-GAIN-APPREC>      0 

<PER-SHARE-DIVIDEND>         0 

<PER-SHARE-DISTRIBUTIONS>    0 

<RETURNS-OF-CAPITAL>         0 

<PER-SHARE-NAV-END>          0 

<EXPENSE-RATIO>              0 

<AVG-DEBT-OUTSTANDING>       0 

<AVG-DEBT-PER-SHARE>         0 



</TABLE>


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