UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number: 811-09713

Active Assets Institutional Money Trust
(Exact name of registrant as specified in charter)

522 Fifth Avenue, New York, New York 10036
(Address of principal executive offices) (Zip code)

Ronald E. Robison
522 Fifth Avenue, New York, New York 10036
(Name and address of agent for service)

Registrant's telephone number, including area code: 212-296-6990

Date of fiscal year end: June 30, 2008

Date of reporting period: December 31, 2007

Item 1 - Report to Shareholders

Welcome, Shareholder:
In this report, you'll learn about how your investment in Active Assets
Institutional Money Trust performed during the semiannual period. We will
provide an overview of the market conditions, and discuss some of the factors
that affected performance during the reporting period. In addition, this report
includes the Fund's financial statements and a list of Fund investments.

THIS MATERIAL MUST BE PRECEDED OR ACCOMPANIED BY A PROSPECTUS FOR THE FUND BEING
OFFERED.

MARKET FORECASTS PROVIDED IN THIS REPORT MAY NOT NECESSARILY COME TO PASS. THERE
IS NO ASSURANCE THAT A MUTUAL FUND WILL ACHIEVE ITS INVESTMENT OBJECTIVE. AN
INVESTMENT IN A MONEY MARKET FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL
DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY. ALTHOUGH THE FUND
SEEKS TO PRESERVE THE VALUE OF AN INVESTMENT AT $1.00 PER SHARE, IT IS POSSIBLE
TO LOSE MONEY BY INVESTING IN THE FUND. PLEASE SEE THE PROSPECTUS FOR MORE
COMPLETE INFORMATION ON INVESTMENT RISKS.

FUND REPORT

For the six months ended December 31, 2007

MARKET CONDITIONS

Throughout most of the fiscal period under review, the majority of home sales
and housing-related statistics were consistently lower than expected. New home
sales for the month of November reached the lowest level since April 1995. U.S.
economic growth, as measured by gross domestic product (GDP), rose 4.9 percent
in the third quarter of 2007, well above the 3.8 percent posted during the
second quarter. Despite the strong third-quarter GDP growth, the unemployment
rate rose slightly for the six-month period. High energy costs, volatile
financial markets and weak housing conditions all contributed to a decline in
consumer confidence during the period.

Financial markets grew increasingly volatile during the reporting period as the
fallout from the troubles in the subprime mortgage sector spread across the
broader fixed income and lending markets. Citing deteriorating financial market
conditions and the negative impact that tighter credit conditions could have in
restraining economic growth, the Federal Open Market Committee (the "Fed")
reduced its federal funds target rate 50 basis points in September, with
additional reductions of 25 basis points in both October and December. At its
December 11 meeting, the Fed noted that strains in financial markets increased
in recent weeks and that incoming data suggested economic growth was slowing. On
December 12, seeking to further improve credit market liquidity, the Fed
announced the creation of a Term Auction Facility (TAF) whereby term funds would
be auctioned to depository institutions against a wide variety of collateral.
TAF auctions are likely to continue for as long as credit market conditions
warrant.

PERFORMANCE ANALYSIS

As of December 31, 2007, Active Assets Institutional Money Trust had net assets
of approximately $1.7 billion and an average portfolio maturity of 51 days. For
the six-month period ended December 31, 2007, the Fund provided a total return
of 2.59 percent. For the seven-day period ended December 31, 2007, the Fund
provided an effective annualized yield of 4.96 percent and a current yield of
4.84 percent, while its 30-day moving average yield for December was 4.87
percent. Past performance is no guarantee of future results.

Our strategy in managing the portfolio remained consistent with the Fund's long-
term focus on preservation of capital and liquidity. Over the past six months,
we sought to maintain the Fund's weighted average maturity primarily in the mid-
50-day range given our expectation that the Fed would continue to reduce its
target funds rate in order to improve credit market liquidity and to help insure
that housing market deterioration would not spillover into the broader economy.
We made purchases in the three-month and longer segment of the money market
curve, emphasizing the deposit liabilities and senior obligations of strong
financial institutions and corporations. We barbelled these three-month and
longer term trades with purchases of overnight repurchase agreements and two-
month and shorter traditional asset backed commercial paper.

There is no guarantee that any sectors mentioned will continue to perform as
discussed herein or that securities in such sectors will be held by the Fund in
the future.

<Table>
<Caption>
PORTFOLIO COMPOSITION

Commercial Paper 37.5%
Certificates of Deposit 29.4
Repurchase Agreements 20.7
Floating Rate Notes 7.0
U.S. Government Agencies 4.2
Short-Term Bank Note 0.9
Corporate Bond Note 0.3
</Table>

<Table>
<Caption>
MATURITY SCHEDULE

1-30 Days 35.9%
31-60 Days 28.3
61-90 Days 17.0
91-120 Days 9.2
121+ Days 9.6
</Table>

Data as of December 31, 2007. Subject to change daily. All percentages for
portfolio composition and maturity schedule are as a percentage of total
investments. These data are provided for informational purposes only and should
not be deemed a recommendation to buy or sell the securities mentioned. Morgan
Stanley is a full-service securities firm engaged in securities trading and
brokerage activities, investment banking, research and analysis, financing and
financial advisory services.

INVESTMENT STRATEGY

THE FUND INVESTS IN HIGH QUALITY, SHORT-TERM DEBT OBLIGATIONS. IN SELECTING
INVESTMENTS, THE FUND'S "INVESTMENT ADVISER," MORGAN STANLEY INVESTMENT ADVISORS
INC., SEEKS TO MAINTAIN THE FUND'S SHARE PRICE AT $1.00. THE SHARE PRICE
REMAINING STABLE AT $1.00 MEANS THAT THE FUND WOULD PRESERVE THE PRINCIPAL VALUE
OF YOUR INVESTMENT.

AN INVESTMENT IN THE FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT
INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY. ALTHOUGH THE FUND SEEKS TO
PRESERVE THE VALUE OF YOUR INVESTMENT AT $1.00 PER SHARE, IT IS POSSIBLE TO LOSE
MONEY BY INVESTING IN THE FUND.

FOR MORE INFORMATION ABOUT PORTFOLIO HOLDINGS

EACH MORGAN STANLEY FUND PROVIDES A COMPLETE SCHEDULE OF PORTFOLIO HOLDINGS IN
ITS SEMIANNUAL AND ANNUAL REPORTS WITHIN 60 DAYS OF THE END OF THE FUND'S SECOND
AND FOURTH FISCAL QUARTERS. THE SEMIANNUAL REPORTS AND THE ANNUAL REPORTS ARE
FILED ELECTRONICALLY WITH THE SECURITIES AND EXCHANGE COMMISSION (SEC) ON FORM
N-CSRS AND FORM N-CSR, RESPECTIVELY. MORGAN STANLEY ALSO DELIVERS THE SEMIANNUAL
AND ANNUAL REPORTS TO FUND SHAREHOLDERS AND MAKES THESE REPORTS AVAILABLE ON ITS
PUBLIC WEB SITE, WWW.MORGANSTANLEY.COM. EACH MORGAN STANLEY FUND ALSO FILES A
COMPLETE SCHEDULE OF PORTFOLIO HOLDINGS WITH THE SEC FOR THE FUND'S FIRST AND
THIRD FISCAL QUARTERS ON FORM N-Q. MORGAN STANLEY DOES NOT DELIVER THE REPORTS
FOR THE FIRST AND THIRD FISCAL QUARTERS TO SHAREHOLDERS, NOR ARE THE REPORTS
POSTED TO THE MORGAN STANLEY PUBLIC WEB SITE. YOU MAY, HOWEVER, OBTAIN THE FORM
N-Q FILINGS (AS WELL AS THE FORM N-CSR AND N-CSRS FILINGS) BY ACCESSING THE
SEC'S WEB SITE, HTTP://WWW.SEC.GOV. YOU MAY ALSO REVIEW AND COPY THEM AT THE
SEC'S PUBLIC

REFERENCE ROOM IN WASHINGTON, DC. INFORMATION ON THE OPERATION OF THE SEC'S
PUBLIC REFERENCE ROOM MAY BE OBTAINED BY CALLING THE SEC AT (800) SEC-0330. YOU
CAN ALSO REQUEST COPIES OF THESE MATERIALS, UPON PAYMENT OF A DUPLICATING FEE,
BY ELECTRONIC REQUEST AT THE SEC'S E-MAIL ADDRESS (PUBLICINFO@SEC.GOV) OR BY
WRITING THE PUBLIC REFERENCE SECTION OF THE SEC, WASHINGTON, DC 20549-0102.

HOUSEHOLDING NOTICE

TO REDUCE PRINTING AND MAILING COSTS, THE FUND ATTEMPTS TO ELIMINATE DUPLICATE
MAILINGS TO THE SAME ADDRESS. THE FUND DELIVERS A SINGLE COPY OF CERTAIN
SHAREHOLDER DOCUMENTS, INCLUDING SHAREHOLDER REPORTS, PROSPECTUSES AND PROXY
MATERIALS, TO INVESTORS WITH THE SAME LAST NAME WHO RESIDE AT THE SAME ADDRESS.
YOUR PARTICIPATION IN THIS PROGRAM WILL CONTINUE FOR AN UNLIMITED PERIOD OF TIME
UNLESS YOU INSTRUCT US OTHERWISE. YOU CAN REQUEST MULTIPLE COPIES OF THESE
DOCUMENTS BY CALLING (800) 869-NEWS, 8:00 A.M. TO 8:00 P.M., ET. ONCE OUR
CUSTOMER SERVICE CENTER HAS RECEIVED YOUR INSTRUCTIONS, WE WILL BEGIN SENDING
INDIVIDUAL COPIES FOR EACH ACCOUNT WITHIN 30 DAYS.

EXPENSE EXAMPLE

As a shareholder of the Fund, you incur ongoing costs, including advisory fees
and other Fund expenses. This example is intended to help you understand your
ongoing costs (in dollars) of investing in the Fund and to compare these costs
with the ongoing costs of investing in other mutual funds.

The example is based on an investment of $1,000 invested at the beginning of the
period and held for the entire period 07/01/07 - 12/31/07.

ACTUAL EXPENSES

The first line of the table below provides information about actual account
values and actual expenses. You may use the information in this line, together
with the amount you invested, to estimate the expenses that you paid over the
period. Simply divide your account value by $1,000 (for example, an $8,600
account value divided by $1,000 = 8.6), then multiply the result by the number
in the first line under the heading entitled "Expenses Paid During Period" to
estimate the expenses you paid on your account during this period.

HYPOTHETICAL EXAMPLE FOR COMPARISON PURPOSES

The second line of the table below provides information about hypothetical
expenses based on the Fund's actual expense ratio and an assumed rate of return
of 5% per year before expenses, which is not the Fund's actual return. The
hypothetical account values and expenses may not be used to estimate the actual
ending account balance or expenses you paid for the period. You may use this
information to compare the ongoing cost of investing in the Fund and other
funds. To do so, compare this 5% hypothetical example with the 5% hypothetical
examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your
ongoing costs only. Therefore, the second line of the table is useful in
comparing ongoing costs, and will not help you determine the relative total cost
of owning different funds that have transactional costs, such as sales charges
(loads), and redemption fees, or exchange fees.

<Table>
<Caption>
BEGINNING ENDING EXPENSES PAID
ACCOUNT VALUE ACCOUNT VALUE DURING PERIOD*
------------- ------------- --------------
07/01/07 -
07/01/07 12/31/07 12/31/07
------------- ------------- --------------

Actual (2.59% return).......................... $1,000.00 $1,025.90 $0.92
Hypothetical (5% annual return before
expenses).................................... $1,000.00 $1,024.30 $0.92
</Table>

- ---------
* Expenses are equal to the Fund's annualized expense ratio of 0.18% multiplied
by the average account value over the period, multiplied by 184/365 (to
reflect the one-half year period).

Active Assets Institutional Money Trust
PORTFOLIO OF INVESTMENTS - DECEMBER 31, 2007 (UNAUDITED)

<Table>
<Caption>
ANNUALIZED
PRINCIPAL YIELD
AMOUNT IN ON DATE OF MATURITY
THOUSANDS DESCRIPTION PURCHASE DATE VALUE
- ----------------------------------------------------------------------------------------------------

Commercial Paper (37.4%)

Asset-Backed - Auto (1.6%)
$ 21,890 DaimlerChrysler Revolving Auto
Conduit LLC Series I........... 4.96 - 5.88% 01/14/08 - 02/08/08 $ 21,794,317
5,000 New Center Asset Trust........... 6.15 01/22/08 4,983,028
--------------
26,777,345
--------------
Asset-Backed - Consumer (5.3)
19,000 CAFCO LLC*....................... 4.92 02/12/08 18,894,835
21,000 Gemini Securitization Corp.,
LLC*........................... 5.39 - 5.49 02/27/08 - 02/28/08 20,823,024
40,000 Old Line Funding, LLC*........... 5.39 - 6.03 01/16/08 - 02/27/08 39,758,111
11,000 Sheffield Receivables Corp.*..... 5.38 03/12/08 10,886,639
--------------
90,362,609
--------------
Asset-Backed - Corporate (2.0%)
21,000 CIESCO LLC*...................... 4.94 03/26/08 20,762,350
3,000 Nieuw Amsterdam Receivables
Corp.*......................... 6.35 01/29/08 2,985,825
10,000 Variable Funding Capital Co.,
LLC*........................... 4.97 02/20/08 9,933,306
--------------
33,681,481
--------------
Asset-Backed - Diversified (2.4%)
10,615 Fairway Finance Co., LLC*........ 6.28 01/11/08 10,598,414
20,000 Hannover Funding Company LLC*.... 5.36 01/11/08 19,973,900
10,000 Three Pillars Funding LLC*....... 5.17 02/15/08 9,937,667
--------------
40,509,981
--------------
Asset-Backed - Securities (6.8%)
11,000 Amstel Funding Corp.*............ 5.52 02/21/08 10,916,736
10,000 Galleon Capital LLC*............. 6.43 01/08/08 9,989,333
30,000 Grampian Funding LLC*............ 5.10 - 5.25 02/01/08 - 02/04/08 29,863,483
65,100 Scaldis Capital LLC*............. 5.10 - 5.50 01/22/08 - 03/04/08 64,539,528
--------------
115,309,080
--------------
Banking (4.7%)
5,000 Bank of America Corp. ........... 4.99 03/25/08 4,943,744
26,000 Citigroup Funding Inc. .......... 4.84 - 5.50 03/11/08 - 05/06/08 25,717,358
24,000 HSBC USA Inc. ................... 4.76 04/14/08 23,680,013
25,000 JPMorgan Chase & Co. ............ 5.13 - 5.14 02/04/08 - 02/05/08 24,882,258
--------------
79,223,373
--------------
Financial Conglomerates (1.2%)
20,000 General Electric Capital Corp. .. 5.26 02/08/08 19,894,139
--------------
</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
PORTFOLIO OF INVESTMENTS - DECEMBER 31, 2007 (UNAUDITED) continued

Insurance (0.5%)
$ 8,000 ING America Insurance Holding
Inc. .......................... 5.02 % 03/28/08 $ 7,905,400
--------------

International Banks (12.9%)
9,325 Bank of Montreal................. 5.07 04/16/08 9,190,642
21,500 Barclays U.S. Funding LLC........ 5.04 - 5.15 02/15/08 - 02/21/08 21,359,013
20,000 Canadian Imperial Holdings....... 4.78 03/12/08 19,817,028
5,000 DnB NOR Bank ASA................. 4.80 03/31/08 4,941,408
35,000 Dexia Delaware LLC............... 4.85 - 4.91 02/15/08 - 02/19/08 34,785,911
10,000 KBC Financial Products
International*................. 4.90 05/23/08 9,811,456
25,000 Natexis Banques Populaires U.S.
Finance Co., LLC............... 5.13 02/12/08 24,856,500
27,000 Royal Bank of Scotland plc....... 4.88 - 4.93 04/28/08 - 05/28/08 26,526,060
42,000 Santander Central Hispano Finance
(Delaware) Inc. ............... 4.73 - 5.14 03/28/08 - 06/02/08 41,298,572
10,000 Societe Generale N.A., Inc. ..... 4.91 04/21/08 9,852,417
15,000 UBS Finance (Delaware) LLC....... 4.96 04/30/08 14,759,273
--------------
217,198,280
--------------
Total Commercial Paper (Cost $630,861,688)............................. 630,861,688
--------------
Certificates of Deposit (29.4%)
Domestic Banks (1.8%)
20,000 Union Bank of California, NA..... 4.70 - 4.80 02/13/08 - 03/31/08 20,000,000
10,000 Wachovia Bank, NA................ 4.90 04/30/08 10,000,000
--------------
30,000,000
--------------
International Banks (27.6%)
16,000 Abbey National Treasury.......... 4.72 01/31/08 16,000,127
3,000 BNP Paribas...................... 5.14 02/08/08 3,000,117
9,000 Bank of Montreal - Chicago....... 5.09 04/18/08 9,000,000
30,000 Bank of Scotland................. 4.85 - 5.00 03/14/08 - 06/11/08 29,998,439
47,000 Barclays Bank plc................ 4.70 - 5.50 01/22/08 - 04/25/08 47,000,425
70,000 Calyon........................... 4.76 - 5.11 01/24/08 - 03/25/08 69,999,960
7,000 Canadian Imperial Bank........... 4.70 04/30/08 6,998,787
25,000 Credit Suisse - NY............... 5.46 03/12/08 25,000,000
18,500 Deutsche Bank AG................. 5.16 01/22/08 18,500,369
15,000 HBOS Treasury Services plc....... 5.12 01/08/08 14,999,864
41,000 NATIXIS.......................... 4.73 - 5.15 02/04/08 - 03/31/08 41,002,546
40,000 Royal Bank of Scotland plc....... 4.70 - 5.17 02/11/08 - 04/30/08 40,001,739
11,000 Skandinaviska Enskilda Banken
AB............................. 4.85 01/25/08 11,001,037
16,000 Societe Generale................. 4.95 - 5.08 03/20/08 - 04/04/08 16,000,000
18,800 Svenska Handelsbanken............ 5.13 04/07/08 18,800,000
</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
PORTFOLIO OF INVESTMENTS - DECEMBER 31, 2007 (UNAUDITED) continued

$ 38,000 Toronto Dominion Bank............ 4.86 - 5.13% 02/29/08 - 06/20/08 $ 38,000,000
59,000 UBS AG........................... 4.95 - 5.47 02/27/08 - 05/05/08 58,999,000
--------------
464,302,410
--------------
Total Certificates of Deposit (Cost $494,302,410)....................... 494,302,410
--------------
Repurchase Agreements (20.6%)
75,000 BNP Paribas Securities Corp.
(dated 12/31/07; proceeds
$75,019,167) (a)............... 4.60 01/02/08 75,000,000
50,000 Banc of America Securities, LLC
(dated 12/31/07; proceeds
$50,012,917) (b)............... 4.65 01/02/08 50,000,000
182,650 Barclays Capital, Inc. (dated
12/31/07; proceeds
$182,695,663) (c).............. 4.50 01/02/08 182,650,000
40,000 Deutsche Bank Securities, Inc.
(dated 12/31/07; proceeds
$40,011,111) (d)............... 5.00 01/02/08 40,000,000
--------------
Total Repurchase Agreements (Cost $347,650,000)......................... 347,650,000
--------------
Floating Rate Notes (7.0%)

Asset-Backed - Structured
Investment Vehicles (1.5%)
15,000 Beta Finance*.................... 5.15+ 01/08/08# 15,000,756
5,000 CC USA Inc.*..................... 4.37+ 01/02/08# 5,000,046
5,000 Cullinan Finance Corp.*.......... 4.32+ 01/02/08# 4,999,944
--------------
25,000,746
--------------
Domestic Banks (0.5%)
9,000 Wachovia Bank, NA................ 4.85+ 03/27/08# 8,985,645
--------------
Finance-Auto (0.9%)
15,000 American Honda Finance Corp.*.... 4.87+ 02/06/08# 15,000,000
--------------
Financial Conglomerates (0.6%)
10,000 General Electric Capital Corp. .. 5.29+ 01/15/08# 10,000,311
--------------
International Banks (3.5%)
15,000 Banco Bilbao Vizcaya Argentaria.. 5.18+ 01/03/08# 14,998,671
10,000 Caja de Ahorros y Monte de Piedad
de Madrid*..................... 5.35+ 01/22/08# 10,000,000
10,000 NATIXIS.......................... 4.77+ 03/31/08# 9,999,172
13,500 UniCredito Italiano SpA.......... 4.86+ 02/06/08# 13,498,155
10,000 Westpac Banking Corp. ........... 4.97+ 01/29/08# 9,999,956
--------------
58,495,954
--------------
Total Floating Rate Notes (Cost $117,482,656)........................... 117,482,656
--------------
</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
PORTFOLIO OF INVESTMENTS - DECEMBER 31, 2007 (UNAUDITED) continued

U.S. Government Agencies (4.2%)
$ 10,000 Federal Farm Credit Bank......... 4.31 % 01/29/08 $ 9,967,975
44,000 Federal Home Loan Banks.......... 4.23 - 5.05 01/02/08 - 06/13/08 43,691,303
17,000 Federal National Mortgage
Association.................... 4.40 - 4.79 02/06/08 - 04/23/08 16,860,661
--------------
Total U.S. Government Agencies (Cost $70,519,939)....................... 70,519,939
--------------
Short-Term Bank Note (0.9%)
15,000 Bank of America, NA (Cost
$15,000,000)................... 4.75 04/07/08 15,000,000
--------------
Corporate Bond Note (0.3%)
Asset-Backed - Structured
Investment Vehicles
5,000 Cullinan Finance Corp.* (Cost
$5,000,000).................... 5.45 02/01/08 5,000,000
--------------
Total Investments (Cost $1,680,816,693) (e)....... 99.8% 1,680,816,693
Other Assets in Excess of Liabilities............. 0.2 3,995,749
------------------- --------------
Net Assets........................................ 100.0% $1,684,812,442
=================== ==============

</Table>

- ----------

<Table>

* Resale is restricted to qualified institutional investors.
+ Rate shown is the rate in effect at December 31, 2007.
# Date of next interest rate reset.
(a) Collateralized by Starbird Funding Corp. 5.85% due 01/02/08 valued at
$76,500,476.
(b) Collateralized by Pasa Funding Ltd. 5.26% due 01/14/08 valued at
$51,000,000.
(c) Collateralized by Freddie Mac 5.45% due 01/22/16 valued at
$67,174,467 and Federal Home Loan Bank 4.90% due 12/04/08 valued at
$119,132,825.
(d) Collateralized by LMC Ltd. 5.38% due 06/01/17 valued at $10,781,606
and Diogenes CDO Ltd. 5.54% due 12/15/43 valued at $8,431,683 and
Deutsche Financial Capital Securitization LLC 7.28% due 09/15/27
valued at $10,514,679 and Reed Elsevier Capital 7.50% due 05/15/25
valued at $11,072,033.
(e) Cost is the same for federal income tax purposes.
</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
FINANCIAL STATEMENTS continued

Statement of Assets and Liabilities
December 31, 2007 (unaudited)

<Table>

Assets:
Investments in securities, at value (cost
$1,680,816,693)
(including repurchase agreements of
$347,650,000).............................. $1,680,816,693
Cash......................................... 138,406
Interest receivable.......................... 8,516,166
Prepaid expenses and other assets............ 74,124
--------------
Total Assets.............................. 1,689,545,389
--------------
Liabilities:
Payable for:
Investments purchased..................... 4,000,000
Dividends to shareholders................. 446,829
Investment advisory fee................... 145,511
Administration fee........................ 72,756
Transfer agent fee........................ 3
Accrued expenses and other payables.......... 67,848
--------------
Total Liabilities......................... 4,732,947
--------------
Net Assets................................ $1,684,812,442
==============
Composition of Net Assets:
Paid-in-capital.............................. $1,684,714,364
Accumulated undistributed net investment
income..................................... 109,300
Accumulated net realized loss................ (11,222)
--------------
Net Assets................................ $1,684,812,442
==============
Net Asset Value Per Share
1,684,823,664 shares outstanding (unlimited
shares authorized of $.01 par value)......... $1.00
==============

</Table>

Statement of Operations
For the six months ended December 31, 2007 (unaudited)

<Table>

Net Investment Income:
Interest Income.............................. $42,699,091
-----------
Expenses
Investment advisory fee...................... 814,046
Administration fee........................... 407,023
Registration fees............................ 45,092
Professional fees............................ 35,497
Custodian fees............................... 26,778
Shareholder reports and notices.............. 21,990
Trustees' fees and expenses.................. 10,970
Transfer agent fees and expenses............. 3,217
Other........................................ 65,434
-----------
Total Expenses............................ 1,430,047
Less: expense offset......................... (23)
-----------
Net Expenses.............................. 1,430,024
-----------
Net Investment Income..................... 41,269,067
-----------
Net Realized Loss on:
Investments.................................. (84,959)
Net increase from payments by affiliate (Note
3)......................................... 73,737
-----------
Net Realized Loss......................... (11,222)
-----------
Net Increase................................. $41,257,845
===========

</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
FINANCIAL STATEMENTS continued

Statements of Changes in Net Assets

<Table>
<Caption>
FOR THE SIX FOR THE YEAR
MONTHS ENDED ENDED
DECEMBER 31, 2007 JUNE 30, 2007
----------------- --------------
(unaudited)

Increase (Decrease) in Net Assets:
Operations:
Net investment income............................. $ 41,269,067 $ 75,931,588
Net realized gain (loss).......................... (84,959) 375
Net increase from payments by affiliate........... 73,737 --
-------------- --------------
Net Increase................................... 41,257,845 75,931,963
-------------- --------------
Dividends and Distributions to Shareholders from:
Net investment income............................. (41,269,442) (75,931,213)
Net realized gain................................. -- (375)
-------------- --------------
Total Dividends and Distributions.............. (41,269,442) (75,931,588)
-------------- --------------
Net increase from transactions in shares of
beneficial interest............................. 79,712,359 504,238,733
-------------- --------------
Net Increase................................... 79,700,762 504,239,108
Net Assets:
Beginning of period............................... 1,605,111,680 1,100,872,572
-------------- --------------
End of Period
(Including accumulated undistributed net
investment income of $109,300 and $109,675,
respectively)..................................... $1,684,812,442 $1,605,111,680
============== ==============

</Table>

See Notes to Financial Statements

Active Assets Institutional Money Trust
NOTES TO FINANCIAL STATEMENTS - DECEMBER 31, 2007 (UNAUDITED)

1. Organization and Accounting Policies
Active Assets Institutional Money 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, preservation of capital and liquidity. The Fund was organized as
a Massachusetts business trust on November 23, 1999 and commenced operations on
February 15, 2000.

The following is a summary of significant accounting policies:

A. Valuation of Investments -- Portfolio securities are valued at amortized
cost, which approximates market value, in accordance with Rule 2a-7 under the
Act.

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 and premiums are amortized over the life of the
respective securities and are included in interest income. Interest income is
accrued daily.

C. Repurchase Agreements -- The Fund may invest directly with institutions in
repurchase agreements. The Fund's custodian receives the collateral, which is
marked-to-market daily to determine that the value of the collateral does not
decrease below the repurchase price plus accrued interest.

D. Federal Income Tax Policy -- It is the Fund's policy to comply with the
requirements of Subchapter M of the Internal Revenue Code applicable to
regulated investment companies and to distribute substantially all of its
taxable income to its shareholders. Therefore, no federal income tax provision
is required. The Fund files tax returns with the U.S. Internal Revenue Service
and New York. The Fund adopted the provisions of the Financial Accounting
Standards Board ("FASB") Interpretation No 48 ("FIN 48") Accounting for
Uncertainty in Income Taxes, on June 29, 2007. FIN 48 sets forth a minimum
threshold for financial statement recognition of the benefit of a tax position
taken or expected to be taken in a tax return. The implementation of FIN 48 did
not result in any unrecognized tax benefits in the accompanying financial
statements. If applicable, the Fund recognizes interest accrued related to
unrecognized tax benefits in interest expense and penalties in other expenses in
the Statement of Operations. Each of the tax years in the four year period ended
December 31, 2007, remains subject to examination by taxing authorities.

E. Dividends and Distributions to Shareholders -- The Fund records dividends and
distributions to shareholders as of the close of each business day.

Active Assets Institutional Money Trust
NOTES TO FINANCIAL STATEMENTS - DECEMBER 31, 2007 (UNAUDITED) continued

F. Use of Estimates -- 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.

2. Investment Advisory/Administration Agreements
Pursuant to an Investment Advisory Agreement with Morgan Stanley Investment
Advisors Inc. (the "Investment Adviser"), the Fund pays the Investment Adviser
an advisory fee, accrued daily and payable monthly, by applying the annual rate
of 0.10% to the net assets of the Fund determined as of the close of each
business day.

Pursuant to an Administration Agreement with Morgan Stanley Services Company
Inc. (the "Administrator"), an affiliate of the Investment Adviser, the Fund
pays an administration fee, accrued daily and payable monthly, by applying the
annual rate 0.05% to the Fund's daily net assets.

Under an agreement between the Administrator and State Street Bank and Trust
Company ("State Street"), State Street provides certain administrative services
to the Fund. For such services, the Administrator pays State Street a portion of
the fee the Administrator receives from the Fund.

The Investment Adviser and the Administrator have agreed to assume all operating
expenses of the Fund (except for brokerage fees) and to waive the compensation
provided for in the Investment Advisory and Administrative Agreements, as
applicable, to the extent that such expenses and compensation on an annualized
basis exceeds 0.20% of the average daily net assets of the Fund.

3. Security Transactions and Transactions with Affiliates
The cost of purchases and proceeds from sales/maturities of portfolio securities
for the six months ended December 31, 2007, aggregated $36,893,648,258 and
$36,833,582,332, respectively. Included in the aforementioned transactions are
sales with other Morgan Stanley funds of $5,898,953.

On November 23, 2007, the Adviser purchased at amortized cost from the Fund, a
security with a par value of $5,923,000. Although this security remained
eligible under SEC Rule 2a-7 to be held by the Fund, due to deterioration in the
assets underlying this holding, the Adviser believed it appropriate to eliminate
the Fund's exposure to this security by purchasing it from the Fund at amortized
cost. The Adviser sought and received "no action" relief from the SEC staff to
engage in this transaction. Had this security been sold to a third party, the
Fund would have realized a loss of approximately $73,737. As a result, this
estimated loss along with offsetting payments from the Adviser has been
reflected in the Statement of Operations and Statement of Changes in Net Assets.
The net result of

Active Assets Institutional Money Trust
NOTES TO FINANCIAL STATEMENTS - DECEMBER 31, 2007 (UNAUDITED) continued

this transaction, including the purchase of the security at amortized cost by
the Adviser, had no impact on the Fund's net assets, net asset value per share
or net investment income.

Morgan Stanley Trust, an affiliate of the Investment Adviser and Administrator,
is the Fund's transfer agent.

The Fund has an unfunded Deferred Compensation Plan (the "Compensation Plan")
which allows each independent Trustee to defer payment of all, or a portion, of
the fees he or she receives for serving on the Board of Trustees. Each eligible
Trustee generally may elect to have the deferred amounts credited with a return
equal to the total return on one or more of the Morgan Stanley funds that are
offered as investment options under the Compensation Plan.
Appreciation/depreciation and distributions received from these investments are
recorded with an offsetting increase/decrease in the deferred compensation
obligation and do not affect the net asset value of the Fund.

4. 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
DECEMBER 31, 2007 JUNE 30, 2007
----------------- --------------
(unaudited)

Shares sold........................................ 3,704,207,980 6,818,842,295
Shares issued in reinvestment of dividends and
distributions.................................... 41,488,834 75,670,912
-------------- --------------
3,745,696,814 6,894,513,207
Shares redeemed.................................... (3,665,984,455) (6,390,274,474)
-------------- --------------
Net increase in shares outstanding................. 79,712,359 504,238,733
============== ==============

</Table>

5. Expense Offset
The expense offset represents a reduction of the fees and expenses for interest
earned on cash balances maintained by the Fund with the transfer agent.

6. Accounting Pronouncement
In September 2006, Statement of Financial Accounting Standards No. 157, Fair
Value Measurements (SFAS 157), was issued and is effective for fiscal years
beginning after November 15, 2007. SFAS 157 defines fair value, establishes a
framework for measuring fair value and expands disclosures about fair value
measurements. Management is currently evaluating the impact the adoption of SFAS
157 will have on the Fund's financial statement disclosures.

Active Assets Institutional Money 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 JUNE 30,
MONTHS ENDED ----------------------------------------------
DECEMBER 31, 2007 2007 2006 2005 2004 2003
----------------- ------ ------ ------ ------ ------
(unaudited)

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........ 0.026 0.052 0.041 0.021 0.009 0.014

Less dividends from net investment income.... (0.026) (0.052)+ (0.041) (0.021) (0.009)+ (0.014)+
------- -------- ------- ------- -------- --------

Net asset value, end of period............... $1.00 $1.00 $1.00 $1.00 $1.00 $1.00
===== ===== ===== ===== ===== =====

Total Return................................. 2.59%(1)(3) 5.30% 4.20% 2.09% 0.91% 1.37%

Ratios to Average Net Assets:
Total expenses (before expense offset)....... 0.18%(2) 0.18% 0.19% 0.18% 0.18% 0.17%

Net investment income........................ 5.07%(2) 5.18% 4.24% 1.97% 0.91% 1.36%

Supplemental Data:
Net assets, end of period, in millions....... $1,685 $1,605 $1,101 $535 $936 $1,148
</Table>

- ----------

<Table>

+ Includes capital gain distribution of less than $0.001.
(1) Not annualized.
(2) Annualized.
(3) The Adviser fully reimbursed the Fund for the loss incurred resulting from
the disposal of an investment. Without this reimbursement, the total
return was 2.58%. See Note 3.
</Table>

See Notes to Financial Statements

TRUSTEES

Frank L. Bowman
Michael Bozic
Kathleen A. Dennis
James F. Higgins
Dr. Manuel H. Johnson
Joseph J. Kearns
Michael F. Klein
Michael E. Nugent
W. Allen Reed
Fergus Reid

OFFICERS

Michael E. Nugent
Chairperson of the Board

Ronald E. Robison
President and Principal Executive Officer

J. David Germany
Vice President

Dennis F. Shea
Vice President

Amy R. Doberman
Vice President

Carsten Otto
Chief Compliance Officer

Stefanie V. Chang Yu
Vice President

Francis J. Smith
Treasurer and Chief Financial Officer

Mary E. Mullin
Secretary

TRANSFER AGENT

Morgan Stanley Trust
Harborside Financial Center, Plaza Two
Jersey City, New Jersey 07311

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

Deloitte & Touche LLP
Two World Financial Center
New York, New York 10281

LEGAL COUNSEL

Clifford Chance US LLP
31 West 52nd Street
New York, New York 10019

COUNSEL TO THE INDEPENDENT TRUSTEES

Kramer Levin Naftalis & Frankel LLP
1177 Avenue of the Americas
New York, New York 10036

INVESTMENT ADVISER

Morgan Stanley Investment Advisors Inc.
522 Fifth Avenue
New York, New York 10036

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

This report is submitted for the general information of the shareholders of the
Fund. For more detailed information about the Fund, its fees and expenses and
other pertinent information, please read its Prospectus. The Fund's Statement of
Additional Information contains additional information about the Fund, including
its trustees. It is available, without charge, by calling (800) 869-NEWS.

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 LOGO]

MORGAN STANLEY FUNDS

Active Assets
Institutional
Money Trust

Semiannual Report
December 31, 2007

AVISAN
IU08-00774P-Y12/07

Item 2. Code of Ethics.

Not applicable for semiannual reports.

Item 3. Audit Committee Financial Expert.

Not applicable for semiannual reports.

Item 4. Principal Accountant Fees and Services

Not applicable for semiannual reports.

Item 5. Audit Committee of Listed Registrants.

Not applicable for semiannual reports.

Item 6.

Refer to Item 1.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End
Management Investment Companies.

Not applicable for semiannual reports.

Item 8. Portfolio Managers of Closed-End Management Investment Companies

Applicable only to reports filed by closed-end funds.

Item 9. Closed-End Fund Repurchases

Applicable to reports filed by closed-end funds.

Item 10. Submission of Matters to a Vote of Security Holders

Not applicable.

Item 11. Controls and Procedures

(a) The Fund's principal executive officer and principal financial officer have
concluded that the Fund's disclosure controls and procedures are sufficient to
ensure that information required to be disclosed by the Fund in this Form N-CSR
was recorded, processed, summarized and reported within the time periods
specified in the Securities and Exchange Commission's rules and forms, based
upon such officers' evaluation of these controls and procedures as of a date
within 90 days of the filing date of the report.

(b) There were no changes in the registrant's internal control over financial
reporting that occurred during the second fiscal quarter of the period covered
by this report that has materially affected, or is reasonably likely to
materially affect, the registrant's internal control over financial reporting.

Item 12. Exhibits

(a) Code of Ethics - Not applicable for semiannual reports.

(b) A separate certification for each principal executive officer and principal
financial officer of the registrant are attached hereto as part of EX-99.CERT.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the
Investment Company Act of 1940, the registrant has duly caused this report to be
signed on its behalf by the undersigned, thereunto duly authorized.

Active Assets Institutional Money Trust

/s/ Ronald E. Robison
Ronald E. Robison
Principal Executive Officer
February 15, 2008

Pursuant to the requirements of the Securities Exchange Act of 1934 and the
Investment Company Act of 1940, this report has been signed by the following
persons on behalf of the registrant and in the capacities and on the dates
indicated.

/s/ Ronald E. Robison
Ronald E. Robison
Principal Executive Officer
February 15, 2008

/s/ Francis Smith
Francis Smith
Principal Financial Officer
February 15, 2008