MORGAN STANLEY DEAN WITTER US GOVERNMENT SECURITIES TRUST, N-30D, 2000-02-17

MORGAN STANLEY DEAN WITTER US GOVERNMENT SECURITIES TRUST
N-30D, 2000-02-17

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<PAGE>

MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT TWO WORLD TRADE CENTER,
SECURITIES TRUST NEW YORK, NEW YORK 10048
LETTER TO THE SHAREHOLDERS DECEMBER 31, 1999

DEAR SHAREHOLDER:

During the 12-month period ended December 31, 1999, the U.S. economy continued
its path of strength propelled by a rising stock market, low inflation and
unemployment, and the recovery in many overseas economies. With renewed strength
in the world economy and the perceived threat of domestic inflation looming, the
Federal Reserve Board raised the federal funds rate in three steps, from 4.75
percent to 5.50 percent, between June and November.

Interest rates on intermediate-term U.S. Treasuries were highly volatile during
the period. Yields on five-year Treasuries ranged from 4.46 percent to 6.32
percent. On December 31, 1999, the five-year Treasury note was yielding 6.28
percent, compared to 4.54 percent one year earlier.

PERFORMANCE AND PORTFOLIO STRATEGY

For the 12-month period ended December 31, 1999, Morgan Stanley Dean Witter U.S.
Government Securities Trust's Class B shares produced a total return of -0.65
percent, compared to -2.23 percent for the Lehman Brothers U.S. Government Bond
Index. For the same period, the Fund's Class A, C and D shares posted total
returns of -0.26 percent, -0.90 percent and -0.10 percent, respectively. The
performance of the Fund's four share classes varies because of differing
expenses. (The total return figures shown assume the reinvestment of all
distributions and do not reflect the deduction of any applicable sales charges.)
The accompanying chart compares the Fund's performance to that of the Lehman
index.

On December 31, 1999, the Fund's net assets exceeded $4.2 billion, with 63
percent of its portfolio invested in mortgage-backed securities issued by the
Government National Mortgage Association (GNMAs), 24 percent in Treasury
securities and the remaining 13 percent in U.S. government agency securities.

<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
LETTER TO THE SHAREHOLDERS DECEMBER 31, 1999, CONTINUED

As the U.S. economy continued to strengthen and interest rates rose during the
year, the Fund's average maturity was increased modestly, to approximately 7.95
years, by December 31, 1999. The Fund's overweighted exposure to mortgage-backed
securities mitigated the negative effects of 1999's bear market in Treasuries.
Narrower spreads, along with a diminished supply of mortgage-backed securities,
helped the mortgage-backed market outperform both the Treasury and agency
markets as strong sponsorship continued for most of the year from banks and
investors.

LOOKING AHEAD

In the new year, the Fed will be on the alert for possible signs of inflation
and may feel it needs to continue on its path of tighter monetary policy.
Accordingly, adjustments to the Fund's maturity and composition may be made as
conditions warrant and attractive opportunities become available.

We appreciate your ongoing support of Morgan Stanley Dean Witter U.S. Government
Securities Trust and look forward to continuing to serve your investment needs.

Very truly yours,

[SIGNATURE]
CHARLES A. FIUMEFREDDO
CHAIRMAN OF THE BOARD

[SIGNATURE]
MITCHELL M. MERIN
PRESIDENT

2
<PAGE>

MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT
SECURITIES TRUST
FUND PERFORMANCE DECEMBER 31, 1999

EDGAR REPRESENTATION OF DATA POINTS USED IN PRINTED GRAPHIC

<TABLE>
<CAPTION>
GROWTH OF $10,000 -- CLASS B
($ IN THOUSANDS)
<S> <C> <C>
FUND LEHMAN(4)
December 1989 $10,000 $10,000
December 1990 $10,849 $10,872
December 1991 $12,089 $12,538
December 1992 $12,785 $13,444
December 1993 $13,697 $14,877
December 1994 $13,216 $14,374
December 1995 $15,429 $17,011
December 1996 $15,916 $17,482
December 1997 $17,279 $19,158
December 1998 $18,535 $21,045
December 1999 $18,413(3) $20,574
</TABLE>

PAST PERFORMANCE IS NOT PREDICTIVE OF FUTURE RETURNS. PERFORMANCE FOR
CLASS A, CLASS C, AND CLASS D SHARES WILL VARY FROM THE PERFORMANCE OF
CLASS B SHARES SHOWN ABOVE DUE TO DIFFERENCES IN CHARGES AND EXPENSES.

<TABLE>
<CAPTION>
AVERAGE ANNUAL TOTAL RETURNS
----------------------------------------------------------------------------------------------
CLASS B SHARES* CLASS A SHARES+
-------------------------------------------- ---------------------------------------------
PERIOD ENDED 12/31/99 PERIOD ENDED 12/31/99
------------------------- -------------------------
<S> <C> <C> <C> <C> <C>
1 Year -0.65%(1) -5.32%(2) 1 Year -0.26%(1) -4.50%(2)
5 Years 6.86 (1) 6.55 (2) Since Inception (7/28/97) 4.47 (1) 2.61 (2)
10 Years 6.30 (1) 6.30 (2)
</TABLE>

<TABLE>
<CAPTION>
CLASS C SHARES++ CLASS D SHARES#
--------------------------------------------- ---------------------------------------------
PERIOD ENDED 12/31/99 PERIOD ENDED 12/31/99
------------------------- -------------------------
<S> <C> <C> <C> <C> <C>
1 Year -0.90%(1) -1.84%(2) 1 Year -0.10%(1)
Since Inception (7/28/97) 4.23 (1) 4.23 (2) Since Inception (7/28/97) 4.70 (1)
</TABLE>

- ------------------------

(1) Figure shown assumes reinvestment of all distributions and does not reflect
the deduction of any sales charges.
(2) Figure shown assumes reinvestment of all distributions and the deduction of
the maximum applicable sales charge. See the Fund's current prospectus for
complete details on fees and sales charges.
(3) Closing value assuming a complete redemption on December 31, 1999.
(4) The Lehman Brothers General U.S. Government Index is a broad-based measure
of all U.S. Government and U.S. Treasury securities. The Index does not
include any expenses, fees or charges. The Index is unmanaged and should
not be considered an investment.
* The maximum CDSC for Class B shares is 5.0%. The CDSC declines to 0% after
six years.
+ The maximum front-end sales charge for Class A shares is 4.25%.
++ The maximum CDSC for Class C shares is 1% for shares redeemed within one
year of purchase.
# Class D shares have no sales charge.

3
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
PORTFOLIO OF INVESTMENTS DECEMBER 31, 1999

<TABLE>
PRINCIPAL DESCRIPTION
AMOUNT IN AND COUPON
THOUSANDS MATURITY DATE RATE VALUE
- ------------------------------------------------------------------------------------------------------------------------
<C> <S> <C> <C>
MORTGAGE-BACKED SECURITIES (63.3%)
Government National Mortgage Assoc. I (61.4%)
$ 121,940 02/15/28 - 03/15/29................................................................. 6.00% $ 111,003,153
343,986 10/15/22 - 09/15/29................................................................. 6.50 323,024,592
1,147,153 04/15/17 - 03/15/27................................................................. 7.00 1,108,078,373
480,110 11/15/02 - 06/15/27................................................................. 7.50 474,859,153
157,975 10/15/16 - 07/15/26................................................................. 8.00 159,555,165
153,661 07/15/06 - 04/15/25................................................................. 8.50 157,982,774
113,902 10/15/08 - 08/15/21................................................................. 9.00 119,170,311
72,865 10/15/09 - 12/15/20................................................................. 9.50 77,601,215
81,915 11/15/09 - 11/15/20................................................................. 10.00 88,928,511
247 05/15/10 - 06/15/15................................................................. 12.50 280,591
--------------
2,620,483,838
--------------

Government National Mortgage Assoc. II (1.8%)
32,845 01/20/24 - 02/20/24................................................................. 6.50 30,740,941
49,253 03/20/26 - 07/20/29................................................................. 7.00 47,421,511
--------------
78,162,452
--------------

Government National Mortgage Assoc. GPM I (0.1%)
3,085 08/15/13 - 07/15/15................................................................. 12.25 3,549,885
--------------

TOTAL MORTGAGE-BACKED SECURITIES
(IDENTIFIED COST $2,749,717,549)............................................................ 2,702,196,175
--------------

U.S. GOVERNMENT OBLIGATIONS (23.7%)
U.S. Treasury Notes (6.3%)
18,000 05/31/03............................................................................ 5.50 17,523,000
118,000 08/15/07............................................................................ 6.125 114,995,720
75,000 02/15/07............................................................................ 6.25 73,761,750
1,050 09/30/01............................................................................ 6.375 1,052,069
5,500 10/15/06............................................................................ 6.50 5,478,550
20,600 04/30/00............................................................................ 6.75 20,667,980
1,800 02/29/00............................................................................ 7.125 1,805,148
30,500 01/31/00............................................................................ 7.75 30,558,560
3,700 02/15/00............................................................................ 8.50 3,713,690
--------------
269,556,467
--------------

U.S. Treasury Principal Strips (17.4%)
13,000 05/15/03............................................................................ 0.00 10,481,250
111,000 02/15/04............................................................................ 0.00 85,280,190
380,000 05/15/04............................................................................ 0.00 287,272,400
385,000 08/15/04............................................................................ 0.00 285,820,150
75,000 11/15/04............................................................................ 0.00 54,756,000
26,000 02/15/05............................................................................ 0.00 18,641,480
--------------
742,251,470
--------------

TOTAL U.S. GOVERNMENT OBLIGATIONS
(IDENTIFIED COST $967,735,179).............................................................. 1,011,807,937
--------------
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS
4
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
PORTFOLIO OF INVESTMENTS DECEMBER 31, 1999, CONTINUED

Resolution Funding Corp. Zero Coupon Strips (11.3%)
109,000 04/15/03............................................................................ 0.00 87,702,490
55,000 07/15/03............................................................................ 0.00 43,629,850
69,000 10/15/03............................................................................ 0.00 53,824,830
89,882 01/15/04............................................................................ 0.00 69,127,347
84,419 04/15/04............................................................................ 0.00 63,445,944
68,000 07/15/04............................................................................ 0.00 50,369,640
1,550 04/15/07............................................................................ 0.00 951,653
18,000 07/15/07............................................................................ 0.00 10,868,040
56,000 10/15/07............................................................................ 0.00 33,089,840
28,000 01/15/08............................................................................ 0.00 16,227,120
20,000 07/15/08............................................................................ 0.00 11,215,000
74,000 10/15/08............................................................................ 0.00 40,798,420
--------------
481,250,174
--------------

Small Business Administration (0.9%)
13,098 Ser 99-D 04/01/19................................................................... 6.15 12,068,910
11,761 Ser 99-F 06/01/19................................................................... 6.80 11,250,061
15,000 Ser 99-G 07/01/19................................................................... 7.00 14,514,900
--------------
37,833,871
--------------

TOTAL U.S. GOVERNMENT AGENCIES
(IDENTIFIED COST $546,690,196).............................................................. 549,807,204
--------------
</TABLE>

<TABLE>
<S> <C> <C>
TOTAL INVESTMENTS
(IDENTIFIED COST $4,264,142,924) (a).................................................... 99.9% 4,263,811,316

CASH AND OTHER ASSETS IN EXCESS OF LIABILITIES.......................................... 0.1 4,420,041
----- ---------------

NET ASSETS.............................................................................. 100.0% $ 4,268,231,357
----- ---------------
----- ---------------
</TABLE>

- ---------------------

GPM Graduated Payment Mortgage.
(a) The aggregate cost for federal income tax purposes approximates identified
cost. The aggregate gross unrealized appreciation is $98,270,536 and the
aggregate gross unrealized depreciation is $98,602,144, resulting in net
unrealized depreciation of $331,608.

SEE NOTES TO FINANCIAL STATEMENTS
5
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL STATEMENTS

STATEMENT OF ASSETS AND LIABILITIES
DECEMBER 31, 1999

<TABLE>
<S> <C>
ASSETS:
Investments in securities, at value
(identified cost $4,264,142,924).......................................................... $4,263,811,316
Cash........................................................................................ 691,483
Receivable for:
Interest................................................................................ 24,610,973
Shares of beneficial interest sold...................................................... 1,597,103
Prepaid expenses and other assets........................................................... 81,192
--------------
TOTAL ASSETS........................................................................... 4,290,792,067
--------------
LIABILITIES:
Payable for:
Dividends and distributions to shareholders............................................. 12,502,945
Shares of beneficial interest repurchased............................................... 5,307,039
Plan of distribution fee................................................................ 2,677,431
Investment management fee............................................................... 1,618,322
Accrued expenses and other payables......................................................... 454,973
--------------
TOTAL LIABILITIES...................................................................... 22,560,710
--------------
NET ASSETS............................................................................. $4,268,231,357
==============
COMPOSITION OF NET ASSETS:
Paid-in-capital............................................................................. $4,930,578,723
Net unrealized depreciation................................................................. (331,608)
Accumulated net realized loss............................................................... (662,015,758)
--------------
NET ASSETS............................................................................. $4,268,231,357
==============
CLASS A SHARES:
Net Assets.................................................................................. $70,881,082
Shares Outstanding (UNLIMITED AUTHORIZED, $.01 PAR VALUE)................................... 8,262,903
NET ASSET VALUE PER SHARE.............................................................. $8.58
==============

MAXIMUM OFFERING PRICE PER SHARE,
(NET ASSET VALUE PLUS 4.44% OF NET ASSET VALUE)...................................... $8.96
==============
CLASS B SHARES:
Net Assets.................................................................................. $4,145,031,101
Shares Outstanding (UNLIMITED AUTHORIZED, $.01 PAR VALUE)................................... 482,475,942
NET ASSET VALUE PER SHARE.............................................................. $8.59
==============
CLASS C SHARES:
Net Assets.................................................................................. $22,004,403
Shares Outstanding (UNLIMITED AUTHORIZED, $.01 PAR VALUE)................................... 2,543,141
NET ASSET VALUE PER SHARE.............................................................. $8.65
==============
CLASS D SHARES:
Net Assets.................................................................................. $30,314,771
Shares Outstanding (UNLIMITED AUTHORIZED, $.01 PAR VALUE)................................... 3,533,820
NET ASSET VALUE PER SHARE.............................................................. $8.58
==============
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS
6
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL STATEMENTS, CONTINUED

STATEMENT OF OPERATIONS
FOR THE YEAR ENDED DECEMBER 31, 1999

<TABLE>
<S> <C>
NET INVESTMENT INCOME:

INTEREST INCOME.............................................................................. $ 338,844,881
-------------

EXPENSES
Plan of distribution fee (Class A shares).................................................... 111,119
Plan of distribution fee (Class B shares).................................................... 34,448,253
Plan of distribution fee (Class C shares).................................................... 165,156
Investment management fee.................................................................... 20,585,209
Transfer agent fees and expenses............................................................. 3,421,055
Custodian fees............................................................................... 814,398
Registration fees............................................................................ 304,325
Shareholder reports and notices.............................................................. 195,852
Professional fees............................................................................ 105,532
Trustees' fees and expenses.................................................................. 18,410
Other........................................................................................ 66,326
-------------

TOTAL EXPENSES.......................................................................... 60,235,635
Less: expense offset......................................................................... (16,496)
Less: plan of distribution fee rebate (Class B shares)....................................... (12,563,961)
-------------
NET EXPENSES............................................................................ 47,655,178
-------------

NET INVESTMENT INCOME................................................................... 291,189,703
-------------

NET REALIZED AND UNREALIZED LOSS:
Net realized loss............................................................................ (5,800,037)
Net change in unrealized appreciation........................................................ (316,259,969)
-------------

NET LOSS................................................................................ (322,060,006)
-------------

NET DECREASE................................................................................. $ (30,870,303)
=============
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS
7
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL STATEMENTS, CONTINUED

STATEMENT OF CHANGES IN NET ASSETS

<TABLE>
FOR THE YEAR FOR THE YEAR
ENDED ENDED
DECEMBER 31, 1999 DECEMBER 31, 1998
- ------------------------------------------------------------------------------------------------------------
<S> <C> <C>

INCREASE (DECREASE)
IN NET ASSETS:

OPERATIONS:
Net investment
income............ $ 291,189,703 $ 310,576,566
Net realized loss... (5,800,037) (2,384,102)
Net change in
unrealized
appreciation...... (316,259,969) 54,569,658
-------------- --------------

NET INCREASE
(DECREASE)..... (30,870,303) 362,762,122
-------------- --------------

DIVIDENDS TO SHAREHOLDERS FROM NET INVESTMENT INCOME:
Class A shares...... (4,445,707) (2,396,071)
Class B shares...... (283,752,269) (306,635,357)
Class C shares...... (1,291,578) (600,619)
Class D shares...... (1,700,149) (944,519)
-------------- --------------

TOTAL
DIVIDENDS...... (291,189,703) (310,576,566)
-------------- --------------
Net decrease from
transactions in
shares of
beneficial
interest.......... (501,912,356) (425,398,131)
-------------- --------------

NET DECREASE... (823,972,362) (373,212,575)

NET ASSETS:
Beginning of
period............ 5,092,203,719 5,465,416,294
-------------- --------------

END OF
PERIOD......... $4,268,231,357 $5,092,203,719
============== ==============
</TABLE>

SEE NOTES TO FINANCIAL STATEMENTS
8
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999

1. ORGANIZATION AND ACCOUNTING POLICIES

Morgan Stanley Dean Witter U.S. Government Securities Trust (the "Fund") is
registered under the Investment Company Act of 1940, as amended (the "Act"), as
a diversified, open-end management investment company. The Fund's investment
objective is high current income consistent with safety of principal. The Fund
seeks to achieve its objective by investing in obligations issued or guaranteed
by the U.S. Government or its instrumentalities. The Fund was organized as a
Massachusetts business trust on September 29, 1983 and commenced operations on
June 29, 1984. On July 28, 1997, the Fund converted to a multiple class share
structure.

The Fund offers Class A shares, Class B shares, Class C shares and Class D
shares. The four classes are substantially the same except that most Class A
shares are subject to a sales charge imposed at the time of purchase and some
Class A shares, and most Class B shares and Class C shares are subject to a
contingent deferred sales charge imposed on shares redeemed within one year, six
years and one year, respectively. Class D shares are not subject to a sales
charge. Additionally, Class A shares, Class B shares and Class C shares incur
distribution expenses.

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 -- (1) all portfolio securities for which
over-the-counter market quotations are readily available are valued at the
latest available bid price prior to the time of valuation; (2) when market
quotations are not readily available, including circumstances under which it is
determined by Morgan Stanley Dean Witter Advisors Inc. (the "Investment
Manager") that sale or bid prices are not reflective of a security's market
value, portfolio securities are valued at their fair value as determined in good
faith under procedures established by and under the general supervision of the
Trustees (valuation of debt securities for which market quotations are not
readily available may be based upon current market prices of securities which
are comparable in coupon, rating and maturity or an appropriate matrix utilizing
similar factors); and (3) certain portfolio securities may be valued by an
outside pricing service approved by the Trustees. The pricing service may
utilize a matrix system incorporating security quality, maturity and coupon as
the evaluation model parameters, and/or research and evaluations by its staff,
including review of broker-dealer market price quotations, if available, in
determining what it believes is the fair valuation of the

9
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999, CONTINUED

securities valued by such pricing service; (4) short-term debt securities having
a maturity date of more than sixty days at time of purchase are valued on a
mark-to-market basis until sixty days prior to maturity and thereafter at
amortized cost based on their value on the 61st day. Short-term debt securities
having a maturity date of sixty days or less at the time of purchase are valued
at amortized cost.

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 by the identified cost method.
Discounts are accreted over the life of the respective securities. Interest
income is accrued daily.

C. MULTIPLE CLASS ALLOCATIONS -- Investment income, expenses (other than
distribution fees), and realized and unrealized gains and losses are allocated
to each class of shares based upon the relative net asset value on the date such
items are recognized. Distribution fees are charged directly to the respective
class.

D. 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 income to its shareholders.
Accordingly, no federal income tax provision is required.

E. DIVIDENDS AND DISTRIBUTIONS TO SHAREHOLDERS -- The Fund records dividends and
distributions to its shareholders on the record date. The amount of dividends
and distributions from net investment income and net realized capital gains are
determined in accordance with federal income tax regulations which may differ
from generally accepted accounting principles. These "book/tax" differences are
either considered temporary or permanent in nature. To the extent these
differences are permanent in nature, such amounts are reclassified within the
capital accounts based on their federal tax-basis treatment; temporary
differences do not require reclassification. Dividends and distributions which
exceed net investment income and net realized capital gains for financial
reporting purposes but not for tax purposes are reported as dividends in excess
of net investment income or distributions in excess of net realized capital
gains. To the extent they exceed net investment income and net realized capital
gains for tax purposes, they are reported as distributions of paid-in-capital.

10
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999, CONTINUED

2. INVESTMENT MANAGEMENT AGREEMENT

Pursuant to an Investment Management Agreement with 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 Fund's net assets
determined at the close of each business day: 0.50% to the portion of daily net
assets not exceeding $1 billion; 0.475% to the portion of daily net assets
exceeding $1 billion but not exceeding $1.5 billion; 0.45% to the portion of
daily net assets exceeding $1.5 billion but not exceeding $2 billion; 0.425% to
the portion of daily net assets exceeding $2 billion but not exceeding
$2.5 billion; 0.40% to the portion of daily net assets exceeding $2.5 billion
but not exceeding $5 billion; 0.375% to the portion of daily net assets
exceeding $5 billion but not exceeding $7.5 billion; 0.35% to the portion of
daily net assets exceeding $7.5 billion but not exceeding $10 billion; 0.325% to
the portion of daily net assets exceeding $10 billion but not exceeding
$12.5 billion; and 0.30% to the portion of daily net assets exceeding
$12.5 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

Shares of the Fund are distributed by Morgan Stanley Dean Witter Distributors
Inc. (the "Distributor"), an affiliate of the Investment Manager. The Fund has
adopted a Plan of Distribution (the "Plan") pursuant to Rule 12b-1 under the
Act. The Plan provides that the Fund will pay the Distributor a fee which is
accrued daily and paid monthly at the following annual rates: (i) Class A -- up
to 0.25% of the average daily net assets of Class A; (ii) Class B -- 0.75%
(0.65% on amounts over $10 billion) of the lesser of: (a) the average daily
aggregate gross sales of the Class B shares since the inception of the Fund (not
including reinvestment of dividend or capital gain distributions) less the
average daily aggregate net asset value of the Class B shares redeemed since the
Fund's inception upon which a contingent deferred sales charge has been imposed
or waived; or (b) the average daily net assets of Class B; and (iii)
Class C -- up to 0.75% of the average daily net assets of Class C. In the case
of Class A shares, amounts paid under the Plan are paid to the Distributor for

11
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999, CONTINUED

services provided. In the case of Class B and Class C shares, amounts paid under
the Plan are paid to the Distributor for (1) services provided and the expenses
borne by it and others in the distribution of the shares of these Classes,
including the payment of commissions for sales of these Classes and incentive
compensation to, and expenses of, Morgan Stanley Dean Witter Financial Advisors
and others who engage in or support distribution of the shares or who service
shareholder accounts, including overhead and telephone expenses; (2) printing
and distribution of prospectuses and reports used in connection with the
offering of these shares to other than current shareholders; and (3)
preparation, printing and distribution of sales literature and advertising
materials. In addition, the Distributor may utilize fees paid pursuant to the
Plan, in the case of Class B shares, to compensate Dean Witter Reynolds Inc.
("DWR"), an affiliate of the Investment Manager and Distributor, and other
selected broker-dealers for their opportunity costs in advancing such amounts,
which compensation would be in the form of a carrying charge on any unreimbursed
expenses.

In the case of Class B shares, provided that the Plan continues in effect, any
cumulative expenses incurred by the Distributor but not yet recovered may be
recovered through the payment of future distribution fees from the Fund pursuant
to the Plan and contingent deferred sales charges paid by investors upon
redemption of Class B shares. Although there is no legal obligation for the Fund
to pay expenses incurred in excess of payments made to the Distributor under the
Plan and the proceeds of contingent deferred sales charges paid by investors
upon redemption of shares, if for any reason the Plan is terminated, the
Trustees will consider at that time the manner in which to treat such expenses.
The Distributor has advised the Fund that there were no excess expenses as of
December 31, 1999.

For the year ended December 31, 1999, the Distributor rebated a portion of the
distribution fees paid by the fund on Class B shares in the amount of
$12,563,961.

In the case of Class A shares and Class C shares, expenses incurred pursuant to
the Plan in any calendar year in excess of 0.25% or 0.75% of the average daily
net assets of Class A or Class C, respectively, will not be reimbursed by the
Fund through payments in any subsequent year, except that expenses representing
a gross sales credit to Morgan Stanley Dean Witter Financial Advisors or other
selected broker-dealer representatives may be reimbursed in the subsequent
calendar year. For the year ended December 31, 1999, the distribution fee was
accrued for Class A shares and Class C shares at the annual rate of 0.16% and
0.75%, respectively.

The Distributor has informed the Fund that for the year ended December 31, 1999
it received contingent deferred sales charges from certain redemptions of the
Fund's Class A shares, Class B

12
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999, CONTINUED

shares and Class C shares of $27,300, $2,612,817 and $24,446, respectively and
received $122,938 in front-end sales charges from sales of the Fund's Class A
shares. The respective shareholders pay such charges which are not an expense of
the Fund.

4. SECURITY TRANSACTIONS AND TRANSACTIONS WITH AFFILIATES

The costs of purchases and proceeds from sales/prepayments of portfolio
securities, excluding short-term investments, for the year ended December 31,
1999 were $505,969,180 and $903,028,342, respectively.

Morgan Stanley Dean Witter Trust FSB, an affiliate of the Investment Manager and
Distributor, is the Fund's transfer agent. At December 31, 1999, the Fund had
transfer agent fees and expenses payable of approximately $96,000.

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 year ended December 31, 1999
included in Trustees' fees and expenses in the Statement of Operations amounted
to $6,077. At December 31, 1999, the Fund had an accrued pension liability of
$54,052 included in accrued expenses in the Statement of Assets and Liabilities.

5. FEDERAL INCOME TAX STATUS

At December 31, 1999, the Fund had a net capital loss carryover of approximately
$661,678,000, which may be used to offset future capital gains to the extent
provided by regulations which is available through December 31 of the following
years:

<TABLE>
<CAPTION>
AMOUNT IN THOUSANDS
- -------------------------------------------------------------------------------------
2000 2001 2002 2003 2004 2005 2006 2007
- -------- -------- -------- -------- -------- -------- -------- --------
<S> <C> <C> <C> <C> <C> <C> <C>
$154,964 $263,492 $118,056 $63,667 $49,153 $3,006 $2,711 $6,629
======== ======== ======== ======= ======= ====== ====== ======
</TABLE>

Capital losses incurred after October 31 ("post-October" losses) within the
taxable year are deemed to arise on the first business day of the Fund's next
taxable year. The Fund incurred and will elect to defer net capital losses of
approximately $169,000 during fiscal 1999.

At December 31, 1999, the Fund had temporary book/tax differences primarily
attributable to post-October losses and capital loss deferrals on wash sales and
permanent book/tax differences attributable to an expired capital loss
carryover. To reflect reclassifications arising from the permanent differences,
paid-in-capital was charged and accumulated net realized loss was credited
$261,525,460.

13
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
NOTES TO FINANCIAL STATEMENTS DECEMBER 31, 1999, CONTINUED

6. SHARES OF BENEFICIAL INTEREST

Transactions in shares of beneficial interest were as follows:

<TABLE>
<CAPTION>
FOR THE YEAR FOR THE YEAR
ENDED ENDED
DECEMBER 31, 1999 DECEMBER 31, 1998
----------------------------- -----------------------------
SHARES AMOUNT SHARES AMOUNT
------------ --------------- ------------ ---------------
<S> <C> <C> <C> <C>
CLASS A SHARES
Sold............................................................. 11,523,348 $ 102,048,487 4,837,972 $ 44,356,004
Reinvestment of dividends........................................ 334,531 2,951,866 145,211 1,330,450
Redeemed......................................................... (9,971,519) (88,017,794) (898,895) (8,228,417)
------------ --------------- ------------ ---------------
Net increase - Class A........................................... 1,886,360 16,982,559 4,084,288 37,458,037
------------ --------------- ------------ ---------------

CLASS B SHARES
Sold............................................................. 82,020,305 731,591,171 103,474,883 948,990,970
Reinvestment of dividends........................................ 17,318,048 153,220,238 17,451,085 159,732,499
Redeemed......................................................... (160,169,929) (1,421,802,486) (173,896,303) (1,593,120,481)
------------ --------------- ------------ ---------------
Net decrease - Class B........................................... (60,831,576) (536,991,077) (52,970,335) (484,397,012)
------------ --------------- ------------ ---------------

CLASS C SHARES
Sold............................................................. 8,354,968 75,105,241 4,818,849 44,609,503
Reinvestment of dividends........................................ 96,528 858,566 41,862 386,582
Redeemed......................................................... (7,754,529) (69,533,325) (3,492,672) (32,338,148)
------------ --------------- ------------ ---------------
Net increase - Class C........................................... 696,967 6,430,482 1,368,039 12,657,937
------------ --------------- ------------ ---------------

CLASS D SHARES
Sold............................................................. 5,347,842 47,178,034 1,554,909 14,290,193
Reinvestment of dividends........................................ 173,200 1,530,121 97,395 892,667
Acquisition of Dean Witter Retirement Series -- U.S. Government
Securities Trust Series......................................... -- -- 986,985 9,087,435
Redeemed......................................................... (4,208,333) (37,042,475) (1,666,314) (15,387,388)
------------ --------------- ------------ ---------------
Net increase - Class D........................................... 1,312,709 11,665,680 972,975 8,882,907
------------ --------------- ------------ ---------------
Net decrease in Fund............................................. (56,935,540) $ (501,912,356) (46,545,033) $ (425,398,131)
============ =============== ============ ===============
</TABLE>

7. ACQUISITION OF DEAN WITTER RETIREMENT SERIES -- U.S. GOVERNMENT SECURITIES
SERIES

As of the close of business on September 11, 1998, the Fund acquired all the net
assets of Dean Witter Retirement Series - U.S. Government Securities Series
("Retirement U.S. Government") pursuant to a plan of reorganization approved by
the shareholders of Retirement U.S. Government on August 19, 1998. The
acquisition was accomplished by a tax-free exchange of 986,985 Class D shares of
the Fund at a net asset value of $9.21 per share for 899,123 shares of
Retirement U.S. Government. The net assets of the Fund and Retirement U.S.
Government immediately before the acquisition were $5,193,431,112 and
$9,087,435, respectively, including unrealized appreciation of $322,808 for
Retirement U.S. Government. Immediately after the acquisition, the combined net
assets of the Fund amounted to $5,202,518,547.

14
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL HIGHLIGHTS

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

<TABLE>
<CAPTION>
FOR THE PERIOD
FOR THE YEAR FOR THE YEAR JULY 28, 1997*
ENDED ENDED THROUGH
DECEMBER 31, 1999 DECEMBER 31, 1998 DECEMBER 31, 1997
- -------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C>
CLASS A SHARES
SELECTED PER SHARE DATA:
Net asset value, beginning of period.................................. $ 9.18 $ 9.09 $ 9.03
------ ------ ------
Income (loss) from investment operations:
Net investment income.............................................. 0.58 0.59 0.25
Net realized and unrealized gain (loss)............................ (0.60) 0.09 0.06
------ ------ ------
Total income (loss) from investment operations........................ (0.02) 0.68 0.31
------ ------ ------
Less dividends from net investment income............................. (0.58) (0.59) (0.25)
------ ------ ------
Net asset value, end of period........................................ $ 8.58 $ 9.18 $ 9.09
====== ====== ======
TOTAL RETURN+......................................................... (0.26)% 7.70% 3.50%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses.............................................................. 0.70%(3) 0.76%(3) 0.77%(2)
Net investment income................................................. 6.50%(3) 6.45%(3) 6.57%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands............................... $70,881 $58,538 $20,841
Portfolio turnover rate............................................... 11% 14% 4%
</TABLE>

- ---------------------

* The date shares were first issued.
+ Does not reflect the deduction of sales charge. Calculated based on the net
asset value as of the last business day of the period.
(1) Not annualized.
(2) Annualized.
(3) Reflects overall Fund ratios for investment income and non-class specific
expenses.

SEE NOTES TO FINANCIAL STATEMENTS
15
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL HIGHLIGHTS, CONTINUED

<TABLE>
<CAPTION>
FOR THE YEAR ENDED DECEMBER 31
----------------------------------------------------------------
1999 1998 1997* 1996 1995
- ---------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
CLASS B SHARES
SELECTED PER SHARE DATA:
Net asset value, beginning of period..................... $ 9.20 $ 9.10 $ 8.92 $ 9.21 $ 8.41
------ ------ ------ ------ ------
Income (loss) from investment operations:
Net investment income................................. 0.55 0.54 0.56 0.56 0.57
Net realized and unrealized gain (loss)............... (0.61) 0.10 0.18 (0.29) 0.80
------ ------ ------ ------ ------
Total income (loss) from investment operations........... (0.06) 0.64 0.74 0.27 1.37
------ ------ ------ ------ ------
Less dividends from net investment income................ (0.55) (0.54) (0.56) (0.56) (0.57)
------ ------ ------ ------ ------
Net asset value, end of period........................... $ 8.59 $ 9.20 $ 9.10 $ 8.92 $ 9.21
====== ====== ====== ====== ======
TOTAL RETURN+............................................ (0.65)% 7.27% 8.56% 3.16% 16.74%
RATIOS TO AVERAGE NET ASSETS:
Expenses................................................. 1.02 %(1)(2) 1.27%(1) 1.26% 1.25% 1.24%
Net investment income.................................... 6.18 %(1)(2) 5.94%(1) 6.22% 6.28% 6.44%
SUPPLEMENTAL DATA:
Net assets, end of period, in millions................... $4,145 $4,996 $5,429 $6,450 $7,955
Portfolio turnover rate.................................. 11 % 14% 4% 8% 14%
</TABLE>

- ---------------------

* Prior to July 28, 1997, the Fund issued one class of shares. All shares of
the Fund held prior to that date, other than shares held by certain
employee benefit plans established by Dean Witter Reynolds Inc. have been
designated Class B shares. Shares held by those employee benefit plans
prior to July 28, 1997 have been designated Class D shares.
+ Does not reflect the deduction of sales charge. Calculated based on the net
asset value as of the last business day of the period.
(1) Reflects overall Fund ratios for investment income and non-class specific
expenses.
(2) If the Distributor had not rebated a portion of its fees to the Fund, the
expense and net investment income ratios would have been 1.29% and 5.91%,
respectively.

SEE NOTES TO FINANCIAL STATEMENTS
16
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL HIGHLIGHTS, CONTINUED

<TABLE>
<CAPTION>
FOR THE PERIOD
FOR THE YEAR FOR THE YEAR JULY 28, 1997*
ENDED ENDED THROUGH
DECEMBER 31, 1999 DECEMBER 31, 1998 DECEMBER 31, 1997
- -------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C>
CLASS C SHARES
SELECTED PER SHARE DATA:
Net asset value, beginning of period.................................. $ 9.26 $ 9.17 $ 9.03
------ ------ ------
Income (loss) from investment operations:
Net investment income.............................................. 0.53 0.55 0.23
Net realized and unrealized gain (loss)............................ (0.61) 0.09 0.14
------ ------ ------
Total income (loss) from investment operations........................ (0.08) 0.64 0.37
------ ------ ------
Less dividends from net investment income............................. (0.53) (0.55) (0.23)
------ ------ ------
Net asset value, end of period........................................ $ 8.65 $ 9.26 $ 9.17
====== ====== ======
TOTAL RETURN+......................................................... (0.90)% 7.14% 4.14%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses.............................................................. 1.29%(3) 1.27%(3) 1.25%(2)
Net investment income................................................. 5.91%(3) 5.94%(3) 5.81%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands............................... $22,004 $17,087 $4,385
Portfolio turnover rate............................................... 11% 14% 4%
</TABLE>

- ---------------------

SEE NOTES TO FINANCIAL STATEMENTS
17
<PAGE>
MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST
FINANCIAL HIGHLIGHTS, CONTINUED

<TABLE>
<CAPTION>
FOR THE PERIOD
FOR THE YEAR FOR THE YEAR JULY 28, 1997*
ENDED ENDED THROUGH
DECEMBER 31, 1999 DECEMBER 31, 1998 DECEMBER 31, 1997
- -------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C>
CLASS D SHARES
SELECTED PER SHARE DATA:
Net asset value, beginning of period.................................. $ 9.18 $ 9.11 $ 9.03
------ ------ ------
Income (loss) from investment operations:
Net investment income.............................................. 0.59 0.61 0.27
Net realized and unrealized gain (loss)............................ (0.60) 0.07 0.08
------ ------ ------
Total income (loss) from investment operations........................ (0.01) 0.68 0.35
------ ------ ------
Less dividends from net investment income............................. (0.59) (0.61) (0.27)
------ ------ ------
Net asset value, end of period........................................ $ 8.58 $ 9.18 $ 9.11
====== ====== ======
TOTAL RETURN+......................................................... (0.10)% 7.72% 3.87%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses.............................................................. 0.54%(3) 0.52%(3) 0.52%(2)
Net investment income................................................. 6.66%(3) 6.69%(3) 6.91%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands............................... $30,315 $20,392 $11,367
Portfolio turnover rate............................................... 11% 14% 4%
</TABLE>

- ---------------------

* The date shares were first issued. Shareholders who held shares of the Fund
prior to July 28, 1997 (the date the Fund converted to a multiple class
share structure) should refer to the Financial Highlights of Class B to
obtain the historical per share data and ratio information of their shares.
+ Calculated based on the net asset value as of the last business day of the
period.
(1) Not annualized.
(2) Annualized.
(3) Reflects overall Fund ratios for investment income and non-class specific
expenses.

SEE NOTES TO FINANCIAL STATEMENTS
18
<PAGE>

MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT
SECURITIES TRUST
REPORT OF INDEPENDENT ACCOUNTANTS

TO THE SHAREHOLDERS AND TRUSTEES
OF MORGAN STANLEY DEAN WITTER U.S. GOVERNMENT SECURITIES TRUST

In our opinion, the accompanying statement of assets and liabilities, including
the portfolio of investments, and the related statements of operations and of
changes in net assets and the financial highlights present fairly, in all
material respects, the financial position of Morgan Stanley Dean Witter U.S.
Government Securities Trust (the "Fund") at December 31, 1999, the results of
its operations for the year then ended, the changes in its net assets for each
of the two years in the period then ended and the financial highlights for each
of the periods indicated, in conformity with accounting principles generally
accepted in the United States. These financial statements and financial
highlights (hereafter referred to as "financial statements") are the
responsibility of the Fund's management; our responsibility is to express an
opinion on these financial statements based on our audits. We conducted our
audits of these financial statements in accordance with auditing standards
generally accepted in the United States, which 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,
assessing the accounting principles used and significant estimates made by
management, and evaluating the overall financial statement presentation. We
believe that our audits, which included confirmation of securities at
December 31, 1999 by correspondence with the custodian, provide a reasonable
basis for the opinion expressed above.

PricewaterhouseCoopers LLP
1177 AVENUE OF THE AMERICAS
NEW YORK, NEW YORK 10036
FEBRUARY 9, 2000

19
<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

Rajesh K. Gupta
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

[graphic]

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
U.S. GOVERNMENT
SECURITIES TRUST
ANNUAL REPORT
DECEMBER 31, 1999