MORGAN STANLEY DEAN WITTER NY MUNI MONEY MARKET TRUST, N-30D, 1999-08-24

MORGAN STANLEY DEAN WITTER NY MUNI MONEY MARKET TRUST
N-30D, 1999-08-24

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<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL
MONEY MARKET TRUST Two World Trade Center,
LETTER TO THE SHAREHOLDERS June 30, 1999 New York, New York 10048

DEAR SHAREHOLDER:

We are pleased to present the semiannual report on the operations of Morgan
Stanley Dean Witter New York Municipal Money Market Trust for the six-month
period ended June 30, 1999.

Tax-free money-market yields moved upward during this period, following the
lead of the taxable money market. This increase in yield reversed the trend of
the latter half of 1998 and reflected the market's response to the persistent
strength in the U.S. economy. The steady release of robust economic data
prompted the Federal Reserve Board to adopt a bias toward higher short-term
interest rates in mid-May. The anticipated Fed tightening became reality at the
end of June when the federal funds rate was increased from 4.75 percent to 5.00
percent. At the same time, however, the Fed reverted to a neutral stance that
appeared to make prospects for another rate hike less likely over the near
term. This had a stabilizing effect on the fixed-income markets.

MUNICIPAL MONEY MARKET OVERVIEW

Within the municipal money market, the trend of interest rates was most
apparent among securities maturing in six months to one year. Early in the
year, one-year yields declined moderately as demand for securities outstripped
supply, but from late February through the end of June, yields moved higher
along with taxable money-market yields. The Bond Buyer One Year Note Index, a
benchmark indicator for the longest maturities in the tax-free money market
sector, registered a net increase of 35 basis points, from 3.04 percent at the
end of December 1998 to 3.39 percent in late June. Nevertheless, one-year
yields as measured by the Index were still 20 basis points lower at the end of
June compared to one year earlier. The ratio of the One Year Note Index to the
yield for one-year U.S. Treasury bills was 66 percent at the end of June,
unchanged from a year earlier. A stable ratio means that performance of
securities in this sector of the municipal market has tracked the performance
of Treasuries with comparable maturities.

<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
LETTER TO THE SHAREHOLDERS June 30, 1999, continued

At the short end of the tax-free money market, interest rates fluctuated in a
wider pattern. Yields for variable-rate demand obligations (VRDOs) with daily
and weekly rate changes were driven primarily by changing cash flows and
fluctuated more widely than yields for longer maturities. Yields for weekly
VRDOs moved over a 180-basis-point range from a low of 2.20 percent in early
February, when cash inflows were strong, to a high of 4.00 percent during tax
season in April. However, during periods when supply and demand were in
balance, the municipal money market yield curve was flat with little difference
between one-year note yields and yields for daily or weekly VRDOs. The average
yield for weekly VRDOs was approximately 3.10 percent for the first half of
1999. This was comparable to the average yield for one-year notes over the same
period.

PERFORMANCE AND PORTFOLIO STRATEGY

Morgan Stanley Dean Witter New York Municipal Money Market Trust's annualized
net investment income ratio was 2.16 percent for the six-month period ended
June 30, 1999. The Fund's thirty-day average yield was 2.26 percent as of June
30, 1999.

On June 30, the Fund's net assets totaled $69.1 million with 63 percent of the
Fund's portfolio invested in VRDOs. New York-exempt commercial paper and
municipal notes, the two other types of securities utilized in the portfolio,
comprised 29 percent and 8 percent of the portfolio, respectively.

Portfolio holdings are continuously reviewed to maintain or improve
creditworthiness. Particular effort is devoted to monitoring the credit quality
of institutions that provide credit enhancement and liquidity facilities for
our investments. The Fund has had no exposure to Asian bank letters of credit
or liquidity facilities for more than three years.

At the end of June the Fund's average maturity was 48 days, up from 32 days at
the end of December. The Fund's weighted average maturity is usually extended
each year between mid-June and early July when newly issued one-year tax and
revenue anticipation notes (TRANs) come to market in large supply. The addition
of longer fixed-rate securities smoothes out portfolio yields by offsetting
some of the yield volatility of VRDOs with daily and weekly rate changes.

LOOKING AHEAD

With the rate change in June the Federal Reserve Board has confirmed its
previously signaled intention of becoming less accommodative in the face of
continued strong domestic economic growth by taking back some of the liquidity
it provided in the fall of 1998. In this environment the Fund's average
maturity will be monitored carefully in order to meet the stated objectives of
stability of principal and liquidity.

2
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
LETTER TO THE SHAREHOLDERS June 30, 1999, continued

On May 1, 1999, Mitchell M. Merin was named President of the Morgan Stanley
Dean Witter Funds. Mr. Merin is the President and Chief Operating Officer of
Asset Management for Morgan Stanley Dean Witter & Co. and President, Chief
Executive Officer and Director of Morgan Stanley Dean Witter Advisors Inc., the
Fund's investment manager. He also serves as Chairman, Chief Executive Officer
and Director of the Fund's distributor and transfer agent.

We appreciate your ongoing support of Morgan Stanley Dean Witter New York
Municipal Money Market Trust and look forward to continuing to serve your
investment objectives.

Very truly yours,

/s/ Charles A. Fiumefreddo /s/ Mitchell M. Merin

CHARLES A. FIUMEFREDDO MITCHELL M. MERIN
Chairman of the Board President

3
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MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
PORTFOLIO OF INVESTMENTS June 30, 1999 (unaudited)

<TABLE>
<CAPTION>
PRINCIPAL
AMOUNT IN COUPON DEMAND
THOUSANDS RATE+ DATE* VALUE
- --------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
NEW YORK TAX-EXEMPT SHORT-TERM VARIABLE RATE MUNICIPAL OBLIGATIONS (64.3%)
Babylon Industrial Development Agency,
$ 1,400 OFS Equity of Babylon Ser 1989 (AMT) .......................................... 3.80% 07/01/99 $ 1,400,000
2,500 Ogden Martin System Ser 1998 (FSA) ............................................ 3.10 07/08/99 2,500,000
1,200 New York City Cultural Resources Trust, Museum of Broadcasting Ser 1989 ........ 3.25 07/08/99 1,200,000
2,700 New York City Housing Development Corporation, James Tower 1994 Ser A .......... 3.15 07/08/99 2,700,000
New York City Industrial Development Agency,
1,000 National Audubon Society Inc Ser 1989 ......................................... 3.35 07/01/99 1,000,000
700 The Calhoun School Inc Ser 1990 ............................................... 3.45 07/08/99 700,000
950 The Columbia Grammar & Preparatory School Ser 1994 ............................ 3.30 07/08/99 950,000
900 New York City Municipal Water Finance Authority, 1994 Ser C (FGIC) ............. 3.70 07/01/99 900,000
2,000 New York City Transitional Finance Authority, Fiscal 1999 Ser A Subser A-1 ..... 3.50 07/08/99 2,000,000
2,200 New York Local Government Assistance Corporation, Ser 1994B .................... 3.25 07/08/99 2,200,000
New York State Dormitory Authority,
800 Cornell University Ser 1990B .................................................. 3.40 07/01/99 800,000
1,500 New York Public Library Ser 1998 B ............................................ 3.25 07/08/99 1,500,000
1,500 Oxford University Press Inc Ser 1993 .......................................... 3.50 07/01/99 1,500,000
1,000 The Metropolitan Museum of Art Ser 1993A ...................................... 3.25 07/08/99 1,000,000
New York State Energy Research & Development Authority,
2,600 Brooklyn Union Gas Co Ser A-2 (MBIA) .......................................... 3.15 07/08/99 2,600,000
3,000 Central Hudson Gas & Electric Corp Ser 1985 B ................................. 3.50 07/08/99 3,000,000
2,000 Electric & Gas 1985 A ......................................................... 3.00 03/15/00 2,000,000
1,300 New York State Electric & Gas Corp Ser 1994 D ................................. 3.80 07/01/99 1,300,000
New York State Housing Finance Agency,
3,000 East 84th Street Ser A (AMT) .................................................. 3.30 07/08/99 3,000,000
2,000 Normandie Court II 1987 Ser A (AMT) ........................................... 3.55 07/08/99 2,000,000
3,000 Service Contract 1998 Ser A ................................................... 3.35 07/08/99 3,000,000
1,000 New York State Medical Care Facilities Finance Agency, Lenox Hill Hospital
1990 Ser A .................................................................... 3.15 07/08/99 1,000,000
1,500 Port Authority of New York & New Jersey, Ser 2 ................................. 3.60 07/01/99 1,500,000
2,000 St Lawrence County Industrial Development Agency, Reynolds Metals Co Ser
1995 (AMT)** .................................................................. 3.20 07/08/99 2,000,000
1,000 Yonkers Industrial Development Agency, Sarah Lawrence College Ser 1997
(MBIA) ........................................................................ 3.20 07/08/99 1,000,000
PUERTO RICO
1,700 Puerto Rico Highway & Transportation Authority, Transportation 1998 Ser A
(AMBAC) ....................................................................... 3.10 07/08/99 1,700,000
-----------
TOTAL NEW YORK TAX-EXEMPT SHORT-TERM VARIABLE RATE MUNICIPAL OBLIGATIONS
(Amortized Cost $44,450,000) ....................................................................... 44,450,000
-----------
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS

4
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MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
PORTFOLIO OF INVESTMENTS June 30, 1999 (unaudited) continued

<TABLE>
<CAPTION>
YIELD TO
PRINCIPAL MATURITY
AMOUNT IN COUPON MATURITY ON DATE OF
THOUSANDS RATE DATE PURCHASE VALUE
- -----------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
NEW YORK TAX-EXEMPT COMMERCIAL PAPER (29.6%)
Long Island Power Authority,
$ 1,000 Electric System Subser 3 ........................... 3.25% 08/31/99 3.25% $ 1,000,000
1,000 Electric System Subser 3 ........................... 3.05 09/09/99 3.05 1,000,000
1,000 Electric System Subser 3 ........................... 3.25 10/13/99 3.25 1,000,000
Metropolitan Transportation Authority,
1,000 Transit Facilities Ser CP-1 Subser A BANs .......... 3.05 10/07/99 3.05 1,000,000
1,000 Transit Facilities Ser CP-1 Subser B BANs .......... 3.05 09/13/99 3.05 1,000,000
1,000 Transit Facilities Ser CP-1 Subser B BANs .......... 3.20 10/14/99 3.20 1,000,000
New York City,
1,000 1994 Ser H Subser H-3 (FSA) ........................ 3.10 08/11/99 3.10 1,000,000
1,000 1994 Ser H Subser H-3 (FSA) ........................ 3.10 08/17/99 3.10 1,000,000
1,500 New York State, Ser V BANs .......................... 3.05 08/12/99 3.05 1,500,000
New York State Dormitory Authority,
1,000 Columbia University 1997 Issue ..................... 3.15 07/14/99 3.15 1,000,000
1,000 Columbia University 1997 Issue ..................... 3.00 08/10/99 3.00 1,000,000
1,000 Columbia University 1997 Issue ..................... 3.30 09/03/99 3.30 1,000,000
New York State Environmental Quality,
1,000 Ser 1997 A ......................................... 2.80 07/28/99 2.80 1,000,000
1,000 Ser 1998 A ......................................... 3.00 08/04/99 3.00 1,000,000
1,000 Ser 1998 A ......................................... 3.10 08/09/99 3.10 1,000,000
New York State Power Authority,
1,000 Ser 2 .............................................. 2.90 07/20/99 2.90 1,000,000
1,000 Ser 2 .............................................. 3.15 08/05/99 3.15 1,000,000
PUERTO RICO
Puerto Rico Government Development Bank,
1,000 Ser 1996 ........................................... 3.00 07/16/99 3.00 1,000,000
1,000 Ser 1996 ........................................... 3.00 09/08/99 3.00 1,000,000
1,000 Ser 1996 ........................................... 2.85 10/19/99 2.85 1,000,000
-----------
TOTAL NEW YORK TAX-EXEMPT COMMERCIAL PAPER
(Amortized Cost $20,500,000) ........................................................ 20,500,000
-----------
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS

5
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MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
PORTFOLIO OF INVESTMENTS June 30, 1999 (unaudited) continued

- ---------------
AMT Alternative Minimum Tax.
BANs Bond Anticipation Notes.
TANs Tax Anticipation Notes.
WI Security purchased on a "when-issued" basis.
+ Rate shown is the rate in effect at June 30, 1999.
* Date on which the principal amount can be recovered through demand.
** This security has been segregated in connection with the purchase of a
"when-issued" security.
(a) Cost is the same for federal income tax purposes.

Bond Insurance:
- ---------------
AMBAC AMBAC Assurance Corporation.
FGIC Financial Guaranty Insurance Company.
FSA Financial Security Assurance Inc.
MBIA Municipal Bond Investors Assurance Corporation.

SEE NOTES TO FINANCIAL STATEMENTS

6
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
FINANCIAL STATEMENTS

STATEMENT OF ASSETS AND LIABILITIES
June 30, 1999 (unaudited)

<TABLE>
<S> <C>
ASSETS:
Investments in securities, at value
(amortized cost $70,968,721) ......................................... $ 70,968,721
Cash ................................................................... 26,533
Interest receivable .................................................... 294,687
Prepaid expenses ....................................................... 7,340
------------
TOTAL ASSETS ......................................................... 71,297,281
------------
LIABILITIES:
Payable for:
Investments purchased ................................................ 1,509,195
Shares of beneficial interest repurchased ............................ 530,171
Investment management fee ............................................ 33,238
Plan of distribution fee ............................................. 6,647
Accrued expenses ....................................................... 69,646
------------
TOTAL LIABILITIES .................................................... 2,148,897
------------
NET ASSETS ........................................................... $ 69,148,384
============
COMPOSITION OF NET ASSETS:
Paid-in-capital ........................................................ $ 69,148,330
Accumulated undistributed net investment income ........................ 54
------------
NET ASSETS ........................................................... $ 69,148,384
============
NET ASSET VALUE PER SHARE,
69,148,330 shares outstanding (unlimited shares authorized of $.01 par
value) ............................................................... $1.00
=====
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS

7
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MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
FINANCIAL STATEMENTS, continued

STATEMENT OF OPERATIONS
For the six months ended June 30, 1999 (unaudited)

<TABLE>
<S> <C>
NET INVESTMENT INCOME:
INTEREST INCOME ................................ $1,122,059
----------
EXPENSES
Investment management fee ...................... 188,667
Plan of distribution fee ....................... 36,717
Professional fees .............................. 31,421
Transfer agent fees and expenses ............... 20,250
Shareholder reports and notices ................ 17,101
Trustees' fees and expenses .................... 9,338
Custodian fees ................................. 3,298
Registration fees .............................. 2,691
Other .......................................... 2,689
----------
TOTAL EXPENSES ............................... 312,172
Less: expense offset ........................... (3,298)
----------
NET EXPENSES ................................. 308,874
----------
NET INVESTMENT INCOME AND NET INCREASE ......... $ 813,185
==========
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS

8
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
FINANCIAL STATEMENTS, continued

STATEMENT OF CHANGES IN NET ASSETS

<TABLE>
<CAPTION>
FOR THE SIX FOR THE YEAR
MONTHS ENDED ENDED
JUNE 30, 1999 DECEMBER 31, 1998
--------------- ------------------
<S> <C> <C>
(unaudited)
INCREASE (DECREASE) IN NET ASSETS:
OPERATIONS:
Net investment income ................................ $ 813,185 $ 1,530,141
Net realized gain .................................... -- 421
----------- -----------
NET INCREASE ....................................... 813,185 1,530,562
Dividends from net investment income ................. (813,200) (1,530,092)
Net increase (decrease) from transactions in shares of
beneficial interest ................................ (7,931,453) 27,743,794
----------- -----------
NET INCREASE (DECREASE) ............................ (7,931,468) 27,744,264

NET ASSETS:
Beginning of period .................................. 77,079,852 49,335,588
----------- -----------
END OF PERIOD
(Including undistributed net investment income of
$54 and $69, respectively) ........................ $69,148,384 $77,079,852
=========== ===========
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS

9
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
NOTES TO FINANCIAL STATEMENTS June 30, 1999 (unaudited)

1. ORGANIZATION AND ACCOUNTING POLICES

Morgan Stanley Dean Witter New York Municipal Money Market Trust (the "Fund"),
is registered under the Investment Company Act of 1940, as amended (the "Act"),
as a non-diversified, open-end management investment company. The Fund's
investment objective is to provide a high level of daily income which is exempt
from federal and New York income tax, consistent with stability of principal
and liquidity. The Fund was organized as a Massachusetts business trust on
December 28, 1989 and commenced operations on March 20, 1990.

The preparation of financial statements in accordance with generally accepted
accounting principles requires management to make estimates and assumptions
that affect the reported amounts and disclosures. Actual results could differ
from those estimates.

The following is a summary of significant accounting policies:

A. VALUATION OF INVESTMENTS -- Portfolio securities are valued at amortized
cost, which approximates market value.

B. ACCOUNTING FOR INVESTMENTS -- Security transactions are accounted for on the
trade date (date the order to buy or sell is executed). Realized gains and
losses on security transactions are determined on the identified cost method.
The Fund amortizes premiums and accretes discounts over the life of the
respective securities. Interest income is accrued daily.

C. FEDERAL INCOME TAX STATUS -- It is the Fund's policy to comply with the
requirements of the Internal Revenue Code applicable to regulated investment
companies and to distribute all of its taxable and nontaxable income to its
shareholders. Accordingly, no federal income tax provision is required.

D. DIVIDENDS AND DISTRIBUTIONS TO SHAREHOLDERS -- The Fund records dividends
and distributions to shareholders as of the close of each business day.

2. INVESTMENT MANAGEMENT AGREEMENT

Pursuant to an Investment Management Agreement with the Morgan Stanley Dean
Witter Advisors Inc. (the "Investment Manager"), the Fund pays the Investment
Manager a management fee, accrued daily and payable monthly, by applying the
following annual rates to the net assets of the Fund determined as of the close
of each business day: 0.50% to the portion of daily net assets not exceeding
$500 million; 0.425% to the portion of daily net assets exceeding $500 million
but not exceeding $750 million; 0.375% to the portion of daily net assets
exceeding $750 million but not exceeding $1 billion; 0.35% to the portion of

10
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
NOTES TO FINANCIAL STATEMENTS June 30, 1999 (unaudited) continued

daily net assets exceeding $1 billion but not exceeding $1.5 billion; 0.325% to
the portion of daily net assets exceeding $1.5 billion but not exceeding $2
billion; 0.30% to the portion of daily net assets exceeding $2 billion but not
exceeding $2.5 billion; 0.275% to the portion of daily net assets exceeding
$2.5 billion but not exceeding $3 billion; and 0.25% to the portion of daily
net assets exceeding $3 billion.

Under the terms of the Agreement, in addition to managing the Fund's
investments, the Investment Manager maintains certain of the Fund's books and
records and furnishes, at its own expense, office space, facilities, equipment,
clerical, bookkeeping and certain legal services and pays the salaries of all
personnel, including officers of the Fund who are employees of the Investment
Manager. The Investment Manager also bears the cost of telephone services,
heat, light, power and other utilities provided to the Fund.

3. PLAN OF DISTRIBUTION

Morgan Stanley Dean Witter Distributors Inc. (the "Distributor"), an affiliate
of the Investment Manager, is the distributor of the Fund's shares and, in
accordance with a Plan of Distribution (the "Plan") pursuant to Rule 12b-1
under the Act, finances certain expenses in connection therewith.

Under the Plan, the Distributor bears the expense of all promotional and
distribution related activities on behalf of the Fund, except for expenses that
the Trustees determine to reimburse, as described below. The following
activities and services may be provided by the Distributor and other
broker-dealers under the Plan: (1) compensation to, and expenses of, Morgan
Stanley Dean Witter Financial Advisors and other selected broker-dealers; (2)
sales incentives and bonuses to sales representatives and to marketing
personnel in connection with promoting sales of the Fund's shares; (3) expenses
incurred in connection with promoting sales of the Fund's shares; (4) preparing
and distributing sales literature; and (5) providing advertising and
promotional activities, including direct mail solicitation and television,
radio, newspaper, magazine and other media advertisements.

The Fund is authorized to reimburse the Distributor for specific expenses the
Distributor incurs or plans to incur in promoting the distribution of the
Fund's shares. The amount of each monthly reimbursement payment may in no event
exceed an amount equal to a payment at the annual rate of 0.15% of the Fund's
average daily net assets during the month. Expenses incurred by the Distributor
pursuant to the Plan in any fiscal year will not be reimbursed by the Fund
through payments accrued in any subsequent fiscal year. For the six months
ended June 30, 1999, the distribution fee was accrued at the annual rate of
0.10%.

11
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
NOTES TO FINANCIAL STATEMENTS June 30, 1999 (unaudited) continued

4. SECURITY TRANSACTIONS AND TRANSACTIONS WITH AFFILIATES

The cost of purchases and proceeds from sales/maturities of portfolio
securities for the six months ended June 30, 1999 aggregated $84,368,540 and
$90,230,000, respectively.

Morgan Stanley Dean Witter Trust FSB, an affiliate of the Investment Manager
and Distributor, is the Fund's transfer agent. At June 30, 1999, the Fund had
transfer agent fees and expenses payable of approximately $400.

The Fund has an unfunded noncontributory defined benefit pension plan covering
all independent Trustees of the Fund who will have served as independent
Trustees for at least five years at the time of retirement. Benefits under this
plan are based on years of service and compensation during the last five years
of service. Aggregate pension costs for the six months ended June 30, 1999
included in Trustees' fees and expenses in the Statement of Operations amounted
to $2,625. At June 30, 1999, the Fund had an accrued pension liability of
$48,652 which is included in accrued expenses in the Statement of Assets and
Liabilities.

5. SHARES OF BENEFICIAL INTEREST

Transactions in shares of beneficial interest, at $1.00 per share, were as
follows:

<TABLE>
<CAPTION>
FOR THE SIX FOR THE YEAR
MONTHS ENDED ENDED
JUNE 30, 1999 DECEMBER 31, 1998
------------- -----------------
<S> <C> <C>
(unaudited)
Shares sold ........................................... 73,841,668 177,790,665
Shares issued in reinvestment of dividends ............ 813,200 1,530,092
---------- -----------
74,654,868 179,320,757
Shares repurchased .................................... (82,586,321) (151,576,963)
----------- ------------
Net increase (decrease) in shares outstanding ......... (7,931,453) 27,743,794
=========== ============
</TABLE>

12
<PAGE>

MORGAN STANLEY DEAN WITTER NEW YORK MUNICIPAL MONEY MARKET TRUST
FINANCIAL HIGHLIGHTS

Selected ratios and per share data for a share of beneficial interest
outstanding throughout each period:

<TABLE>
<CAPTION>
FOR THE SIX FOR THE YEAR ENDED DECEMBER 31,
MONTHS ENDED ------------------------------------------------------------
JUNE 30, 1999 1998 1997 1996 1995 1994
- -------------------------------------------------------------------------------------------------------------------------------
(unaudited)
<S> <C> <C> <C> <C> <C> <C>
SELECTED PER SHARE DATA:
Net asset value, beginning of period .......... $1.00 $1.00 $1.00 $1.00 $1.00 $1.00
----- ----- ----- ----- ----- -----
Net income from investment operations ......... 0.011 0.025 0.026 0.025 0.028 0.018

Less dividends from net investment income ..... (0.011) (0.025) (0.026) (0.025) (0.028) (0.018)
----- ----- ----- ----- ----- -----
Net asset value, end of period ................ $1.00 $1.00 $1.00 $1.00 $1.00 $1.00
===== ===== ===== ===== ===== =====
TOTAL RETURN .................................. 1.08%(1) 2.53% 2.68% 2.53% 2.84% 1.78%

RATIOS TO AVERAGE NET ASSETS:
Expenses ...................................... 0.83%(2)(3) 0.87%(3) 0.96%(3) 0.95%(3) 1.01%(3) 1.03%
Net investment income ......................... 2.16%(2) 2.48% 2.64% 2.48% 2.79% 1.75%

SUPPLEMENTAL DATA:
Net assets, end of period, in thousands ....... $69,148 $77,080 $49,336 $40,758 $39,108 $39,629
</TABLE>

- -------------
(1) Not annualized.
(2) Annualized.
(3) Does not reflect the effect of the expense offset of 0.01%.

SEE NOTES TO FINANCIAL STATEMENTS

13
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<PAGE>

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<PAGE>

TRUSTEES

Michael Bozic
Charles A. Fiumefreddo
Edwin J. Garn
Wayne E. Hedien
Dr. Manuel H. Johnson
Michael E. Nugent
Philip J. Purcell
John L. Schroeder

OFFICERS

Charles A. Fiumefreddo
Chairman and Chief Executive Officer

Mitchell M. Merin
President

Barry Fink
Vice President, Secretary and General Counsel

Katherine H. Stromberg
Vice President

Thomas F. Caloia
Treasurer

TRANSFER AGENT

Morgan Stanley Dean Witter Trust FSB
Harborside Financial Center - Plaza Two
Jersey City, New Jersey 07311

INDEPENDENT ACCOUNTANTS

PricewaterhouseCoopers LLP
1177 Avenue of the Americas
New York, New York 10036

INVESTMENT MANAGER

Morgan Stanley Dean Witter Advisors Inc.
Two World Trade Center
New York, New York 10048

The financial statements included herein have been taken from the records of
the Fund without examination by the independent accountants and accordingly
they do not express an opinion thereon.

This report is submitted for the general information of shareholders of the
Fund. For more detailed information about the Fund, its officers and trustees,
fees, expenses and other pertinent information, please see the prospectus
of the Fund.

This report is not authorized for distribution to prospective investors in the
Fund unless preceded or accompanied by an effective prospectus. Read the
prospectus carefully before investing.

MORGAN STANLEY
DEAN WITTER
NEW YORK MUNICIPAL
MONEY MARKET TRUST

[Graphic]

SEMIANNUAL REPORT
JUNE 30, 1999