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 811-02945
                                                     ---------

                          Centennial Money Market Trust
                          -----------------------------
               (Exact name of registrant as specified in charter)


             6803 South Tucson Way, Centennial, Colorado 80112-3924
             ------------------------------------------------------
               (Address of principal executive offices) (Zip code)

                              Robert G. Zack, Esq.
                             OppenheimerFunds, Inc.
            Two World Financial Center, New York, New York 10281-1008
            ---------------------------------------------------------
                     (Name and address of agent for service)

       Registrant's telephone number, including area code: (303) 768-3200
                                                           --------------

                        Date of fiscal year end: June 30
                                                 -------

                      Date of reporting period: 12/31/2008
                                                ----------


ITEM 1. REPORTS TO STOCKHOLDERS.

December 31, 2008

Centennial                         Semiannual Report and Management Commentaries
Money Market Trust



TRUST EXPENSES

TRUST EXPENSES. As a shareholder of the Trust, you incur ongoing costs,
including management fees; service fees; and other Trust expenses. These
examples are intended to help you understand your ongoing costs (in dollars) of
investing in the Trust and to compare these costs with the ongoing costs of
investing in other mutual funds.

The examples are based on an investment of $1,000.00 invested at the beginning
of the period and held for the entire 6-month period ended December 31, 2008.

ACTUAL EXPENSES. The first section of the table provides information about
actual account values and actual expenses. You may use the information in this
section, together with the amount you invested, to estimate the expense that you
paid over the period. Simply divide your account value by $1,000.00 (for
example, an $8,600.00 account value divided by $1,000.00 = 8.60), then multiply
the result by the number in the first section 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 section of the table
provides information about hypothetical account values and hypothetical expenses
based on the Trust's actual expense ratio, and an assumed rate of return of 5%
per year before expenses, which is not the 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 costs of investing in the Trust 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.


                        3 | CENTENNIAL MONEY MARKET TRUST



TRUST EXPENSES Continued



                                BEGINNING          ENDING             EXPENSES
                                 ACCOUNT          ACCOUNT           PAID DURING
                                  VALUE            VALUE           6 MONTHS ENDED
ACTUAL                        JULY 1, 2008   DECEMBER 31, 2008   DECEMBER 31, 2008
- ------                        ------------   -----------------   -----------------
                                                        
HYPOTHETICAL
(5% return before expenses)     $1,000.00        $1,008.70             $4.77
                                ---------        ---------             -----
                                 1,000.00         1,020.47              4.80


Expenses are equal to the Trust's annualized expense ratio, multiplied by the
average account value over the period, multiplied by 184/365 (to reflect the
one-half year period). The annualized expense ratio based on the 6-month period
ended December 31, 2008 is as follows:

EXPENSE RATIO
- -------------
    0.94%

The "Financial Highlights" table in the Trust's financial statements, included
in this report, also show the gross expense ratio, without such waivers or
reimbursements and reduction to custodian expenses, if applicable.


                        4 | CENTENNIAL MONEY MARKET TRUST


STATEMENT OF INVESTMENTS December 31, 2008 / Unaudited



                                                    PRINCIPAL
                                                      AMOUNT          VALUE
                                                   ------------   --------------
                                                            
CERTIFICATES OF DEPOSIT--28.7%
DOMESTIC CERTIFICATES OF DEPOSIT--4.6%
Citibank NA:
1.25%, 1/9/09                                      $ 30,000,000   $   30,000,000
1.85%, 3/12/09                                       50,000,000       50,000,000
                                                                  --------------
                                                                      80,000,000
                                                                  --------------
YANKEE CERTIFICATES OF DEPOSIT--24.1%
Bank of Nova Scotia,
Houston, TX:
0.25%, 1/27/09                                       50,000,000       50,000,000
0.25%, 1/29/09                                       39,000,000       39,000,000
BNP Paribas, New York,
1.97%, 2/12/09                                       32,000,000       32,000,000
Calyon, New York:
0.50%, 1/23/09                                       24,800,000       24,800,000
4.615%, 1/16/09                                      20,000,000       20,031,297
Lloyds TSB Bank plc,
2.50%, 2/2/09                                        81,000,000       81,000,000
Nordea Bank Finland plc, New York,
0.70%, 3/20/09                                       84,000,000       84,000,000
Rabobank Nederland NV, New York:
0.65%, 3/16/09                                       28,000,000       28,000,000
0.75%, 6/30/09                                        2,500,000        2,500,000
Toronto Dominion Bank, New York,
1%, 3/10/09                                          55,000,000       55,000,000
                                                                  --------------
                                                                     416,331,297
                                                                  --------------
Total Certificates of Deposit
   (Cost $496,331,297)                                               496,331,297
                                                                  --------------
DIRECT BANK OBLIGATIONS--18.6%
Calyon North America, Inc.:
0.44%, 1/22/09                                       35,000,000       34,991,017
0.45%, 1/12/09                                        7,000,000        6,999,038
Danske Corp.:
1.20%, 3/19/09                                        2,600,000        2,593,327
1.75%, 3/16/09(1)                                    30,000,000       29,892,083
1.79%, 3/12/09(1)                                     2,000,000        1,991,950
1.80%, 1/5/09(1)                                     50,000,000       49,990,000




                                                    PRINCIPAL
                                                      AMOUNT          VALUE
                                                   ------------   --------------
                                                            
DIRECT BANK OBLIGATIONS Continued
National Australia  Funding (Delaware), Inc.:
0.67%, 3/30/09(1)                                  $ 19,000,000   $   18,968,882
1.47%, 1/15/09(1)                                    41,000,000       40,976,562
1.51%, 2/6/09(1)                                     13,000,000       12,980,370
1.77%, 2/20/09(1)                                     2,000,000        1,995,083
1.83%, 1/7/09(1)                                     15,000,000       14,995,425
Nordea North America, Inc.,
2.04%, 3/11/09                                        1,000,000          996,090
Rabobank USA Financial Corp.,
1.01%, 2/3/09                                        20,000,000       19,981,483
Royal Bank of Canada,
1.13%, 3/9/09                                        85,000,000       84,821,240
                                                                  --------------
Total Direct Bank Obligations
   (Cost $322,172,550)                                               322,172,550
                                                                  --------------
SHORT-TERM NOTES--52.4%
CAPITAL MARKETS--6.9%
Banc of America Securities LLC,
0.19%, 1/1/09(2)                                     70,000,000       70,000,000
BNP Paribas Finance, Inc.,
1.075%, 3/23/09                                      50,000,000       49,879,063
                                                                  --------------
                                                                     119,879,063
                                                                  --------------
DIVERSIFIED FINANCIAL SERVICES--5.1%
General Electric Capital Corp.:
1.90%, 2/10/09                                       40,000,000       39,915,556
2.02%, 2/4/09                                        28,000,000       27,946,582
2.86%, 1/28/09                                       20,000,000       19,957,100
                                                                  --------------
                                                                      87,819,238
                                                                  --------------
INSURANCE--4.7%
Jackson National Life Global Funding,
Series 2004-6,
1.285%, 8/15/09(2, 3)                                50,000,000       50,000,000
MetLife Funding, Inc.,
1%, 1/8/09                                           31,000,000       30,993,972
                                                                  --------------
                                                                      80,993,972
                                                                  --------------



                       F1 | CENTENNIAL MONEY MARKET TRUST



STATEMENT OF INVESTMENTS Unaudited / Continued



                                                    PRINCIPAL
                                                      AMOUNT          VALUE
                                                   ------------   --------------
                                                            
LEASING & FACTORING--5.0%
Toyota Motor Credit Corp.:
1.35%, 1/29/09                                     $ 13,000,000   $   12,986,350
1.70%, 3/16/09                                       71,000,000       70,751,894
2.65%, 1/26/09                                        2,600,000        2,595,215
                                                                  --------------
                                                                      86,333,459
                                                                  --------------
OIL, GAS & CONSUMABLE FUELS--2.9%
Total Capital,
1.10%, 1/5/09(1)                                     50,000,000       49,993,889
                                                                  --------------
PERSONAL PRODUCTS--0.7%
Reckitt Benckiser Treasury Services
plc, 2.30%, 3/3/09(1)                                13,000,000       12,949,336
                                                                  --------------
RECEIVABLES FINANCE--26.1%
Chariot Funding LLC:
0.25%, 1/22/09(4)                                    15,000,000       14,997,813
1.40%, 1/9/09(4)                                     65,000,000       64,979,778
Falcon Asset Securitization Co. LLC:
1.40%, 1/21/09(1)                                    75,000,000       74,941,667
1.40%, 2/11/09(1)                                    10,000,000        9,984,056
Gemini Securitization Corp.:
0.55%, 2/17/09(1)                                     8,401,000        8,394,968
1.70%, 1/7/09(1)                                      2,000,000        1,999,433
1.95%, 2/11/09(1)                                    13,300,000       13,270,463
3.25%, 1/26/09(1)                                    45,000,000       44,898,438
Lexington Parker Capital Co. LLC:
2.20%, 1/13/09(1)                                    23,000,000       22,983,133
2.50%, 1/9/09(1)                                     14,000,000       13,992,222
2.60%, 1/23/09(1)                                    35,000,000       34,944,389
Park Avenue Receivables Co. LLC:
1.40%, 1/6/09                                        34,000,000       33,993,389
1.40%, 1/20/09                                       25,064,000       25,045,480
1.40%, 1/22/09                                       28,191,000       28,167,977
Ranger Funding Co. LLC,
1.55%, 1/5/09(4)                                     10,135,000       10,133,255
Thunder Bay Funding LLC:
1.10%, 1/13/09(4)                                     3,000,000        2,998,900




                                                    PRINCIPAL
                                                      AMOUNT          VALUE
                                                   ------------   --------------
                                                            
RECEIVABLES FINANCE Continued
Thunder Bay Funding LLC: Continued
1.45%, 2/9/09(4)                                   $ 27,000,000   $   26,957,588
3%, 1/28/09(4)                                       18,976,000       18,933,304
                                                                  --------------
                                                                     451,616,253
                                                                  --------------
SPECIAL PURPOSE FINANCIAL--1.0%
Ticonderoga Funding LLC:
0.25%, 1/12/09                                       11,726,000       11,725,104
0.28%, 1/6/09                                         6,400,000        6,399,749
                                                                  --------------
                                                                      18,124,853
                                                                  --------------
Total Short-Term Notes
   (Cost $907,710,063)                                               907,710,063
                                                                  --------------
TOTAL INVESTMENTS, AT VALUE
   (COST $1,726,213,910)                                   99.7%   1,726,213,910
OTHER ASSETS NET OF LIABILITIES                             0.3        4,732,916
                                                   ------------   --------------
NET ASSETS                                                100.0%  $1,730,946,826
                                                   ============   ==============


FOOTNOTES TO STATEMENT OF INVESTMENTS

SHORT-TERM NOTES AND DIRECT BANK OBLIGATIONS ARE GENERALLY TRADED ON A DISCOUNT
BASIS; THE INTEREST RATE SHOWN IS THE DISCOUNT RATE RECEIVED BY THE TRUST AT THE
TIME OF PURCHASE. OTHER SECURITIES NORMALLY BEAR INTEREST AT THE RATES SHOWN.

(1.) Security issued in an exempt transaction without registration under the
     Securities Act of 1933. Such securities amount to $460,142,349, or 26.58%
     of the Trust's net assets, and have been determined to be liquid pursuant
     to guidelines adopted by the Board of Trustees.

(2.) Represents the current interest rate for a variable or increasing rate
     security.

(3.) Illiquid security. The aggregate value of illiquid securities as of
     December 31, 2008 was $50,000,000, which represents 2.89% of the Trust's
     net assets. See Note 4 of accompanying Notes.

(4.) Represents securities sold under Rule 144A, which are exempt from
     registration under the Securities Act of 1933, as amended. These securities
     have been determined to be liquid under guidelines established by the Board
     of Trustees. These securities amount to $139,000,638 or 8.03% of the
     Trust's net assets as of December 31, 2008.


                       F2 | CENTENNIAL MONEY MARKET TRUST



VALUATION INPUTS

Various data inputs are used in determining the value of each of the Trust's
investments as of the reporting period end. These data inputs are categorized in
the following hierarchy under applicable financial accounting standards:

     1) Level 1--quoted prices in active markets for identical assets or
     liabilities (including securities actively traded on a securities exchange)

     2) Level 2--inputs other than quoted prices that are observable for the
     asset (such as quoted prices for similar assets and market corroborated
     inputs such as interest rates, prepayment speeds, credit risks, etc.)

     3) Level 3--unobservable inputs (including the Manager's own judgments
     about assumptions that market participants would use in pricing the asset).

The market value of the Trust's investments was determined based on the
following inputs as of December 31, 2008:



                                               INVESTMENTS IN   OTHER FINANCIAL
VALUATION DESCRIPTION                            SECURITIES       INSTRUMENTS*
- ---------------------                          --------------   ----------------
                                                          
Level 1--Quoted Prices                         $           --         $--
Level 2--Other Significant Observable Inputs    1,726,213,910          --
Level 3--Significant Unobservable Inputs                   --          --
                                               --------------         ---
Total                                          $1,726,213,910         $--
                                               ==============         ===


*    Other financial instruments include options written, currency contracts,
     futures, forwards and swap contracts. Currency contracts and forwards are
     reported at their unrealized appreciation/depreciation at measurement date,
     which represents the change in the contract's value from trade date.
     Futures are reported at their variation margin at measurement date, which
     represents the amount due to/from the Trust at that date. Options written
     and swaps are reported at their market value at measurement date.

SEE THE ACCOMPANYING NOTES FOR FURTHER DISCUSSION OF THE METHODS USED IN
DETERMINING VALUE OF THE TRUST'S INVESTMENTS, AND A SUMMARY OF CHANGES TO THE
VALUATION TECHNIQUES, IF ANY, DURING THE REPORTING PERIOD.

SEE ACCOMPANYING NOTES TO FINANCIAL STATEMENTS.


                       F3 | CENTENNIAL MONEY MARKET TRUST


STATEMENT OF ASSETS AND LIABILITIES Unaudited



December 31, 2008
- -----------------
                                                              
ASSETS
Investments, at value (cost $1,726,213,910)--
   see accompanying statement of investments                     $1,726,213,910
Cash                                                                  8,217,677
Receivables and other assets:
Shares of beneficial interest sold                                  134,773,380
Interest                                                                791,083
Other                                                                   621,043
                                                                 --------------
Total assets                                                      1,870,617,093
                                                                 --------------
LIABILITIES
Payables and other liabilities:
Shares of beneficial interest redeemed                              137,562,061
Transfer and shareholder servicing agent fees                         1,798,044
Distribution and service plan fees                                      194,171
Trustees' compensation                                                   36,864
Shareholder communications                                               20,786
Dividends                                                                 2,955
Other                                                                    55,386
                                                                 --------------
Total liabilities                                                   139,670,267
                                                                 --------------
NET ASSETS                                                       $1,730,946,826
                                                                 ==============
COMPOSITION OF NET ASSETS
Paid-in capital                                                  $1,730,951,228
Accumulated net realized loss on investments                             (4,402)
                                                                 --------------
NET ASSETS--applicable to 1,731,411,199 shares
   of beneficial interest outstanding                            $1,730,946,826
                                                                 ==============
NET ASSET VALUE, REDEMPTION PRICE PER SHARE
   AND OFFERING PRICE PER SHARE                                  $         1.00


SEE ACCOMPANYING NOTES TO FINANCIAL STATEMENTS.


                       F4 | CENTENNIAL MONEY MARKET TRUST



STATEMENT OF OPERATIONS Unaudited



For the Six Months Ended December 31, 2008
- ------------------------------------------
                                                                 
INVESTMENT INCOME
Interest                                                            $36,930,941
                                                                    -----------
EXPENSES
Management fees                                                       5,436,197
Transfer and shareholder servicing agent fees                         3,804,546
Service plan fees                                                     2,680,212
Registration and filing fees                                            555,578
Insurance expense                                                       240,158
Shareholder communications                                              217,095
Trustees' compensation                                                   50,953
Legal, auditing and other professional fees                              27,156
Other                                                                   123,714
                                                                    -----------
Total expenses                                                       13,135,609
                                                                    -----------
NET INVESTMENT INCOME                                                23,795,332
NET REALIZED GAIN ON INVESTMENTS                                        145,760
                                                                    -----------
NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS                $23,941,092
                                                                    ===========


SEE ACCOMPANYING NOTES TO FINANCIAL STATEMENTS.


                       F5 | CENTENNIAL MONEY MARKET TRUST



STATEMENTS OF CHANGES IN NET ASSETS



                                                           SIX MONTHS            YEAR
                                                             ENDED               ENDED
                                                       DECEMBER 31, 2008       JUNE 30,
                                                          (UNAUDITED)            2008
                                                       -----------------   ----------------
                                                                     
OPERATIONS
Net investment income                                   $    23,795,332    $    782,617,133
Net realized gain                                               145,760              94,929
                                                        ---------------    ----------------
Net increase in net assets resulting from operations         23,941,092         782,712,062
DIVIDENDS AND/OR DISTRIBUTIONS TO SHAREHOLDERS
Dividends from net investment income                        (23,795,332)       (782,617,133)
Distributions from net realized gain                           (228,396)            (14,582)
BENEFICIAL INTEREST TRANSACTIONS
Net decrease in net assets resulting from beneficial
   interest transactions                                 (3,706,880,337)    (16,247,383,928)
NET ASSETS
Total decrease                                           (3,706,962,973)    (16,247,303,581)
                                                        ---------------    ----------------
Beginning of period                                       5,437,909,799      21,685,213,380
                                                        ---------------    ----------------
End of period                                           $ 1,730,946,826    $  5,437,909,799
                                                        ===============    ================


SEE ACCOMPANYING NOTES TO FINANCIAL STATEMENTS.


                       F6 | CENTENNIAL MONEY MARKET TRUST


FINANCIAL HIGHLIGHTS



                                                           SIX MONTHS
                                                              ENDED                           YEAR ENDED JUNE 30,
                                                        DECEMBER 31, 2008   -------------------------------------------------------
                                                           (UNAUDITED)        2008        2007        2006        2005        2004
                                                        -----------------   -------     -------     -------     -------     -------
                                                                                                          
PER SHARE OPERATING DATA
Net asset value, beginning of period                        $ 1.00          $  1.00     $  1.00     $  1.00     $  1.00     $  1.00
Income from investment operations--
   net investment income and net realized gain                 .01(1)           .04(1)      .05(1)      .04(1)      .02(1)      .01
Dividends and/or distributions to shareholders:
Dividends from net investment income                          (.01)            (.04)       (.05)       (.04)       (.02)       (.01)
Distributions from net realized gain                            --(2)            --(2)       --(2)       --          --          --
                                                            ------          -------     -------     -------     -------     -------
Total dividends and/or distributions to shareholders          (.01)            (.04)       (.05)       (.04)       (.02)       (.01)
                                                            ------          -------     -------     -------     -------     -------
Net asset value, end of period                              $ 1.00          $  1.00     $  1.00     $  1.00     $  1.00     $  1.00
                                                            ======          =======     =======     =======     =======     =======
TOTAL RETURN(3)                                               0.87%            3.79%       4.80%       3.70%       1.59%       0.61%
                                                            ======          =======     =======     =======     =======     =======
RATIOS/SUPPLEMENTAL DATA
Net assets, end of period (in millions)                     $1,731          $ 5,438     $21,685     $22,424     $20,307     $21,191
Average net assets (in millions)                            $2,759          $20,415     $24,003     $21,527     $20,966     $22,509
Ratios to average net assets:(4)
Net investment income                                         1.71%            3.83%       4.71%       3.62%       1.57%       0.61%
Total expenses                                                0.94%            0.71%       0.66%       0.67%       0.68%       0.67%
Expenses after payments, waivers and/or
   reimbursements and reduction to custodian expenses         0.94%            0.71%       0.66%       0.67%       0.68%       0.51%


(1.) Per share amounts calculated based on the average shares outstanding during
     the period.

(2.) Less than $0.005 per share.

(3.) Assumes an investment on the business day before the first day of the
     fiscal period, with all dividends and distributions reinvested in
     additional shares on the reinvestment date, and redemption at the net asset
     value calculated on the last business day of the fiscal period. Total
     returns are not annualized for periods less than one full year. Returns do
     not reflect the deduction of taxes that a shareholder would pay on trust
     distributions or the redemption of trust shares.

(4.) Annualized for periods less than one full year.

SEE ACCOMPANYING NOTES TO FINANCIAL STATEMENTS.


                       F7 | CENTENNIAL MONEY MARKET TRUST



NOTES TO FINANCIAL STATEMENTS Unaudited

1. SIGNIFICANT ACCOUNTING POLICIES

Centennial Money Market Trust (the "Trust") is registered under the Investment
Company Act of 1940, as amended, as an open-end management investment company.
The Trust's investment objective is to seek the maximum current income that is
consistent with low capital risk and the maintenance of liquidity. The Trust's
investment advisor is Centennial Asset Management Corporation (the "Manager"), a
subsidiary of OppenheimerFunds, Inc. ("OFI").

     The following is a summary of significant accounting policies consistently
followed by the Trust.

SECURITIES VALUATION. The net asset value of shares of the Trust is normally
determined twice each day, at Noon Eastern time and at 4:00 P.M. Eastern time on
each day the New York Stock Exchange (the "Exchange") is open for trading.
Securities are valued at cost adjusted by the amortization of discount or
premium to maturity (amortized cost), which approximates market value. If
amortized cost is determined not to approximate market value, the fair value of
the portfolio securities will be determined under procedures approved by the
Trust's Board of Trustees.

     Effective for fiscal periods beginning after November 15, 2007, FASB
Statement of Financial Accounting Standards No. 157, FAIR VALUE MEASUREMENTS,
establishes a hierarchy for measuring fair value of assets and liabilities. As
required by the standard, each investment asset or liability of the Trust is
assigned a level at measurement date based on the significance and source of the
inputs to its valuation. Quoted prices in active markets for identical
securities are classified as "Level 1", inputs other than quoted prices for an
asset that are observable are classified as "Level 2" and unobservable inputs,
including the Manager's judgment about the assumptions that a market participant
would use in pricing an asset or liability are classified as "Level 3". The
inputs used for valuing securities are not necessarily an indication of the
risks associated with investing in those securities. A table summarizing the
Trust's investments under these levels of classification is included following
the Statement of Investments.

     "Money market-type" instruments are typically designated as Level 2.

     In the absence of a readily available quoted market price, including for
securities whose values have been materially affected by what the Manager
identifies as a significant event occurring before the Trust's assets are valued
but after the close of the securities' respective exchanges, the Manager, acting
through its internal valuation committee, in good faith determines the fair
valuation of that asset using consistently applied procedures under the
supervision of the Board of Trustees (which reviews those fair valuations by the
Manager). Those procedures include certain standardized methodologies to fair
value securities. Such methodologies include, but are not limited to, pricing
securities initially at cost and subsequently adjusting the value based on:
changes in company specific fundamentals, changes in an appropriate securities
index, or changes in the value of similar securities which may be adjusted for
any discounts related to resale restrictions. When possible, such methodologies
use observable market inputs such as quoted prices of similar securities,
observable


                       F8 | CENTENNIAL MONEY MARKET TRUST



interest rates, currency rates and yield curves. The methodologies used for
valuing securities are not necessarily an indication of the risks associated
with investing in those securities.

     Fair valued securities may be classified as "Level 3" if the valuation
primarily reflects the Manager's own assumptions about the inputs that market
participants would use in valuing such securities.

     There have been no significant changes to the fair valuation methodologies
during the period.

FEDERAL TAXES. The Trust intends to comply with provisions of the Internal
Revenue Code applicable to regulated investment companies and to distribute
substantially all of its investment company taxable income to shareholders.
Therefore, no federal income or excise tax provision is required. The Trust
files income tax returns in U.S. federal and applicable state jurisdictions. The
statute of limitations on the Trust's tax return filings generally remain open
for the three preceding fiscal reporting period ends.

     Net investment income (loss) and net realized gain (loss) may differ for
financial statement and tax purposes. The character of dividends and
distributions made during the fiscal year from net investment income or net
realized gains may differ from their ultimate characterization for federal
income tax purposes. Also, due to timing of dividends and distributions, the
fiscal year in which amounts are distributed may differ from the fiscal year in
which the income or net realized gain was recorded by the Trust.

TRUSTEES' COMPENSATION. The Board of Trustees has adopted a compensation
deferral plan for independent trustees that enables trustees to elect to defer
receipt of all or a portion of the annual compensation they are entitled to
receive from the Trust. For purposes of determining the amount owed to the
Trustee under the plan, deferred amounts are treated as though equal dollar
amounts had been invested in shares of the Trust or in other Oppenheimer funds
selected by the Trustee. The Trust purchases shares of the funds selected for
deferral by the Trustee in amounts equal to his or her deemed investment,
resulting in a Trust asset equal to the deferred compensation liability. Such
assets are included as a component of "Other" within the asset section of the
Statement of Assets and Liabilities. Deferral of trustees' fees under the plan
will not affect the net assets of the Trust, and will not materially affect the
Trust's assets, liabilities or net investment income per share. Amounts will be
deferred until distributed in accordance to the compensation deferral plan.

DIVIDENDS AND DISTRIBUTIONS TO SHAREHOLDERS. Dividends and distributions to
shareholders, which are determined in accordance with income tax regulations and
may differ from U.S. generally accepted accounting principles, are recorded on
the ex-dividend date. Income distributions, if any, are declared daily and paid
monthly. Capital gain distributions, if any, are declared and paid annually but
may be paid at other times to maintain the net asset value per share at $1.00.

INVESTMENT INCOME. Interest income is recognized on an accrual basis. Discount
and premium, which are included in interest income on the Statement of
Operations, are amortized or accreted daily.


                       F9 | CENTENNIAL MONEY MARKET TRUST


NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

1. SIGNIFICANT ACCOUNTING POLICIES Continued

CUSTODIAN FEES. "Custodian fees and expenses" in the Statement of Operations may
include interest expense incurred by the Trust on any cash overdrafts of its
custodian account during the period. Such cash overdrafts may result from the
effects of failed trades in portfolio securities and from cash outflows
resulting from unanticipated shareholder redemption activity. The Trust pays
interest to its custodian on such cash overdrafts, to the extent they are not
offset by positive cash balances maintained by the Trust, at a rate equal to the
Federal Funds Rate plus 0.50%. The "Reduction to custodian expenses" line item,
if applicable, represents earnings on cash balances maintained by the Trust
during the period. Such interest expense and other custodian fees may be paid
with these earnings.

SECURITY TRANSACTIONS. Security transactions are recorded on the trade date.
Realized gains and losses on securities sold are determined on the basis of
identified cost.

INDEMNIFICATIONS. The Trust's organizational documents provide current and
former trustees and officers with a limited indemnification against liabilities
arising in connection with the performance of their duties to the Trust. In the
normal course of business, the Trust may also enter into contracts that provide
general indemnifications. The Trust's maximum exposure under these arrangements
is unknown as this would be dependent on future claims that may be made against
the Trust. The risk of material loss from such claims is considered remote.

OTHER. The preparation of financial statements in conformity with accounting
principles generally accepted in the United States of America requires
management to make estimates and assumptions that affect the reported amounts of
assets and liabilities and disclosure of contingent assets and liabilities at
the date of the financial statements and the reported amounts of increases and
decreases in net assets from operations during the reporting period. Actual
results could differ from those estimates.

2. SHARES OF BENEFICIAL INTEREST

The Trust has authorized an unlimited number of no par value shares of
beneficial interest. Transactions in shares of beneficial interest were as
follows:



                                      SIX MONTHS ENDED
                                     DECEMBER 31, 2008                 YEAR ENDED JUNE 30, 2008
                              --------------------------------   ----------------------------------
                                  SHARES           AMOUNT             SHARES            AMOUNT
                              --------------   ---------------   ---------------   ----------------
                                                                       
Sold                           5,541,341,085   $ 5,541,341,085    53,292,947,992   $ 53,292,947,992
Dividends and/or
   distributions reinvested        5,674,534         5,674,534       197,940,894        197,940,894
Redeemed                      (9,253,895,956)   (9,253,895,956)  (69,738,272,814)   (69,738,272,814)
                              --------------   ---------------   ---------------   ----------------
Net decrease                  (3,706,880,337)  $(3,706,880,337)  (16,247,383,928)  $(16,247,383,928)
                              ==============   ===============   ===============   ================



                      F10 | CENTENNIAL MONEY MARKET TRUST



3. FEES AND OTHER TRANSACTIONS WITH AFFILIATES

MANAGEMENT FEES. Under the investment advisory agreement, the Trust pays the
Manager a management fee based on the daily net assets of the Trust at an annual
rate as shown in the following table:



FEE SCHEDULE
- ------------
                  
Up to $250 million   0.500%
Next $250 million    0.475
Next $250 million    0.450
Next $250 million    0.425
Next $250 million    0.400
Next $250 million    0.375
Next $500 million    0.350
Over $2 billion      0.325


TRANSFER AGENT FEES. Shareholder Services, Inc. ("SSI") acts as the transfer and
shareholder servicing agent for the Trust. The Trust pays SSI a per account fee.
For the six months ended December 31, 2008, the Trust paid $10,773,830 to SSI
for services to the Trust.

SERVICE PLAN (12B-1) FEES. The Trust has adopted a Service Plan (the "Plan"). It
reimburses Centennial Asset Management Corporation (the "Distributor"), for a
portion of its costs incurred for services provided to accounts that hold shares
of the Trust. Reimbursement is made periodically depending on asset size, at an
annual rate of up to 0.20% of the average annual net assets of the Trust. The
Distributor currently uses all of those fees (together with significant amounts
from the Manager's own resources) to pay dealers, brokers, banks and other
financial institutions periodically for providing personal service and
maintenance of accounts of their customers that hold shares of the Trust. Fees
incurred by the Trust under the Plan are detailed in the Statement of
Operations.

WAIVERS AND REIMBURSEMENTS OF EXPENSES. The Manager has voluntarily undertaken
to waive fees to the extent necessary to assist the Trust in attempting to
maintain a positive yield. There is no guarantee that the Trust will maintain a
positive yield. That undertaking may be amended or withdrawn at any time.

     SSI has voluntarily agreed to limit transfer and shareholder servicing
agent fees to 0.35% of average annual net assets of the Trust. This undertaking
may be amended or withdrawn at any time.

4. ILLIQUID SECURITIES

As of December 31, 2008, investments in securities included issues that are
illiquid. Investments may be illiquid because they do not have an active trading
market, making it difficult to value them or dispose of them promptly at an
acceptable price. The Trust will not invest more than 10% of its net assets
(determined at the time of purchase and reviewed periodically) in illiquid
securities. Securities that are illiquid are marked with an applicable footnote
on the Statement of Investments.


                      F11 | CENTENNIAL MONEY MARKET TRUST



NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

5. TEMPORARY GUARANTEE PROGRAM FOR MONEY MARKET FUNDS

The Trust's Board of Trustees has elected for the Trust to participate in the
Temporary Guarantee Program for Money Market Funds (the "Program") established
by the U.S. Treasury Department. The Treasury Department has accepted the
Trust's application to participate in the Program and entered into a Guarantee
Agreement with the Trust dated as of September 19, 2008. The Trust has also
notified the Treasury Department of its intent to continue its participation in
the Program through April 30, 2009.

     Under the Program, shareholders of the Trust as of the close of business on
September 19, 2008 may be guaranteed against loss in the event that the Trust's
net asset value falls below $0.995. The Program applies only to shareholders of
record as of the close of business on September 19, 2008. The number of shares
covered by the Program will be the lesser of (a) the number of shares of the
Trust owned by the shareholder on September 19, 2008 or (b) the number of shares
owned by the shareholder on the date the Trust's net asset value falls below
$0.995. If the number of shares of the Trust a shareholder holds after September
19, 2008 fluctuates during the Program period due to purchases or redemptions of
shares, any shares in excess of the amount held as of the close of business on
September 19, 2008 will not be covered.

     The Trust has paid a fee to participate in the Program's initial term in
the amount equal to 0.01% of the Trust's net assets as of the close of business
on September 19, 2008. The Trust has paid an additional fee to continue its
participation in the Program through April 30, 2009 in the amount of 0.015% of
the Trust's net assets as of the close of business on September 19, 2008. Fees
paid by the Trust to participate in the Program are shown as insurance expense
on the Statement of Operations. Participation in any further extension of the
Program would require payment of an additional fee.

6. RECENT ACCOUNTING PRONOUNCEMENT

In March 2008, the Financial Accounting Standards Board ("FASB") issued
Statement on Financial Accounting Standards ("SFAS") No. 161, DISCLOSURES ABOUT
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES. This standard requires enhanced
disclosures about derivative and hedging activities, including qualitative
disclosures about how and why the Trust uses derivative instruments, how these
activities are accounted for, and their effect on the Trust's financial
position, financial performance and cash flows. SFAS No. 161 is effective for
financial statements issued for fiscal years and interim periods beginning after
November 15, 2008. At this time, management is evaluating the implications of
SFAS No. 161 and its impact on the Trust's financial statements and related
disclosures.

7. CHANGE IN INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

At a meeting held on August 20, 2008, the Board of Trustees of the Trust
appointed KPMG LLP as the independent registered public accounting firm to the
Trust for fiscal year 2009, replacing the firm of Deloitte & Touche LLP,
effective at the conclusion of the fiscal 2008 audit. During the two most recent
fiscal years the audit reports of Deloitte &


                      F12 | CENTENNIAL MONEY MARKET TRUST



Touche LLP contained no adverse opinion or disclaimer of opinion and were not
qualified or modified as to uncertainty, audit scope or accounting principles.
Further, there were no disagreements between the Trust and Deloitte & Touche LLP
on accounting principles, financial statement disclosure or audit scope, which
if not resolved to the satisfaction of Deloitte & Touche LLP would have caused
it to make reference to the disagreements in connection with its reports.


                      F13 | CENTENNIAL MONEY MARKET TRUST



                      THIS PAGE INTENTIONALLY LEFT BLANK.


                      F14 | CENTENNIAL MONEY MARKET TRUST



BOARD APPROVAL OF THE FUND'S INVESTMENT ADVISORY AGREEMENT Unaudited

Each year, the Board of Trustees (the "Board"), including a majority of the
independent Trustees, is required to determine whether to renew Centennial Money
Market Trust's (the "Fund") investment advisory agreement (the "Agreement"). The
Investment Company Act of 1940, as amended, requires that the Board request and
evaluate, and that the Manager provide, such information as may be reasonably
necessary to evaluate the terms of the Agreement. The Board employs an
independent consultant to prepare a report that provides information, including
comparative information, the Board requests for that purpose. In addition, the
Board receives information throughout the year regarding Fund services, fees,
expenses and performance.

     The Manager and the independent consultant provided information to the
Board on the following factors: (i) the nature, quality and extent of the
Manager's services, (ii) the investment performance of the Fund and the Manager,
(iii) the fees and expenses of the Fund, including comparative expense
information, (iv) the profitability of the Manager and its affiliates, including
an analysis of the cost of providing services, (v) whether economies of scale
are realized as the Fund grows and whether fee levels reflect these economies of
scale for Fund investors and (vi) other benefits to the Manager from its
relationship with the Fund. The Board was aware that there are alternatives to
retaining the Manager.

     Outlined below is a summary of the principal information considered by the
Board as well as the Board's conclusions.

     NATURE, QUALITY AND EXTENT OF SERVICES. The Board considered information
about the nature, quality and extent of the services provided to the Fund and
information regarding the Manager's key personnel who provide such services. The
Manager's duties include providing the Fund with the services of the portfolio
manager and the Manager's investment team, who provide research, analysis and
other advisory services in regard to the Fund's investments; securities trading
services; oversight of third party service providers; monitoring compliance with
applicable Fund policies and procedures and adherence to the Fund's investment
restrictions. The Manager is responsible for providing certain administrative
services to the Fund as well. Those services include providing and supervising
all administrative and clerical personnel who are necessary in order to provide
effective corporate administration for the Fund; compiling and maintaining
records with respect to the Fund's operations; preparing and filing reports
required by the Securities and Exchange Commission; preparing periodic reports
regarding the operations of the Fund for its shareholders; preparing proxy
materials for shareholder meetings; and preparing the registration statements
required by Federal and state securities laws for the sale of the Fund's shares.
The Manager also provides the Fund with office space, facilities and equipment.


                        5 | CENTENNIAL MONEY MARKET TRUST



BOARD APPROVAL OF THE FUND'S INVESTMENT ADVISORY AGREEMENT Unaudited / Continued

     The Board also considered the quality of the services provided and the
quality of the Manager's resources that are available to the Fund. The Board
took account of the fact that the Manager has had over forty years of experience
as an investment adviser and that its assets under management rank it among the
top mutual fund managers in the United States. The Board evaluated the Manager's
advisory, administrative, accounting, legal and compliance services, and
information the Board has received regarding the experience and professional
qualifications of the Manager's key personnel and the size and functions of its
staff. In its evaluation of the quality of the portfolio management services
provided, the Board considered the experience of Carol Wolf, the portfolio
manager for the Fund, and the Manager's investment team and analysts. The Board
members also considered the totality of their experiences with the Manager as
Directors or Trustees of the Fund and other funds advised by the Manager. The
Board considered information regarding the quality of services provided by
affiliates of the Manager, which its members have become knowledgeable about in
connection with the renewal of the Fund's service agreements. The Board
concluded in light of the Manager's experience, reputation, personnel,
operations and resources, the Fund benefits from the services provided under the
Agreement.

     INVESTMENT PERFORMANCE OF THE MANAGER AND THE FUND. Throughout the year,
the Manager provided information on the investment performance of the Fund and
the Manager, including comparative Performance information. The Board also
reviewed information, prepared by the Manager and by the independent consultant,
comparing the Fund's historical performance to relevant market indices and to
the performance of other retail front-end load and no-load money market funds
advised by the manager and other investment advisers. The Board considered that
the Fund outperformed or performed competitively vis-a-vis its performance
universe median during the one-, three-, five- and ten-year periods.

     COSTS OF SERVICES BY THE MANAGER. The Board reviewed the fees paid to the
Manager and the other expenses borne by the Fund. The Board also considered the
comparability of the fees charged and the services provided to the Fund to the
fees and services for other clients or accounts advised by the Manager. The
independent consultant provided comparative data in regard to the fees and
expenses of the Fund and money market funds with comparable asset levels and
distribution features. The Board considered that the Fund's actual management
fees and total expenses were higher than its expense group median.

     ECONOMIES OF SCALE AND PROFITS REALIZED BY THE MANAGER. The Board
considered information regarding the Manager's costs in serving as the Fund's
investment adviser,


                        6 | CENTENNIAL MONEY MARKET TRUST



including the costs associated with the personnel and systems necessary to
manage the Fund, and information regarding the Manager's profitability from its
relationship with the Fund. The Board reviewed whether the Manager may realize
economies of scale in managing and supporting the Fund. The Board noted that the
Fund currently has management fee breakpoints, which are intended to share with
Fund shareholders economies of scale that may exist as the Fund's assets grow.

     OTHER BENEFITS TO THE MANAGER. In addition to considering the profits
realized by the Manager, the Board considered information that was provided
regarding the direct and indirect benefits the Manager receives as a result of
its relationship with the Fund, including compensation paid to the Manager's
affiliates. The Board also considered that the Manager must be able to pay and
retain experienced professional personnel at competitive rates to provide
quality services to the Fund and that maintaining the financial viability of the
Manager is important in order for the Manager to continue to provide significant
services to the Fund and its shareholders.

     CONCLUSIONS. These factors were also considered by the independent Trustees
meeting separately from the full Board, assisted by experienced counsel to the
Fund and to the independent Trustees. Fund counsel and the independent Trustees'
counsel are independent of the Manager within the meaning and intent of the
Securities and Exchange Commission Rules.

     Based on its review of the information it received and its evaluations
described above, the Board, including a majority of the independent Trustees,
decided to continue the Agreement for another year. In arriving at this
decision, the Board did not single out any factor or factors as being more
important than others, but considered all of the above information, and
considered the terms and conditions of the Agreement, including the management
fee, in light of all of the surrounding circumstances.


                        7 | CENTENNIAL MONEY MARKET TRUST



PORTFOLIO PROXY VOTING POLICIES AND PROCEDURES; UPDATES TO STATEMENTS OF
INVESTMENTS Unaudited

The Trust has adopted Portfolio Proxy Voting Policies and Procedures under which
the Trust votes proxies relating to securities ("portfolio proxies") held by the
Trust. A description of the Trust's Portfolio Proxy Voting Policies and
Procedures is available (i) without charge, upon request, by calling the Trust
toll-free at 1.800.525.7048, (ii) on the Trust's website at
www.oppenheimerfunds.com, and (iii) on the SEC's website at www.sec.gov. In
addition, the Trust is required to file Form N-PX, with its complete proxy
voting record for the 12 months ended June 30th, no later than August 31st of
each year. The Trust's voting record is available (i) without charge, upon
request, by calling the Trust toll-free at 1.800.525.7048, and (ii) in the Form
N-PX filing on the SEC's website at www.sec.gov.

     The Trust files its complete schedule of portfolio holdings with the SEC
for the first quarter and the third quarter of each fiscal year on Form N-Q. The
Trust's Form N-Q filings are available on the SEC's website at
http://www.sec.gov. Those forms may be reviewed and copied at the SEC's Public
Reference Room in Washington, D.C. Information on the operation of the Public
Reference Room may be obtained by calling 1-800-SEC-0330.


                        8 | CENTENNIAL MONEY MARKET TRUST



ITEM 2. CODE OF ETHICS.

Not applicable to semiannual reports.

ITEM 3. AUDIT COMMITTEE FINANCIAL EXPERT.

Not applicable to semiannual reports.

ITEM 4. PRINCIPAL ACCOUNTANT FEES AND SERVICES.

Not applicable to semiannual reports.



ITEM 5. AUDIT COMMITTEE OF LISTED REGISTRANTS

Not applicable.

ITEM 6. SCHEDULE OF INVESTMENTS.

a) Not applicable.

b) Not applicable.

ITEM 7. DISCLOSURE OF PROXY VOTING POLICIES AND PROCEDURES FOR CLOSED-END
MANAGEMENT INVESTMENT COMPANIES.

Not applicable.

ITEM 8. PORTFOLIO MANAGERS OF CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable.

ITEM 9. PURCHASES OF EQUITY SECURITIES BY CLOSED-END MANAGEMENT INVESTMENT
COMPANY AND AFFILIATED PURCHASERS.

Not applicable.

ITEM 10. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

THE FUND'S GOVERNANCE COMMITTEE PROVISIONS WITH RESPECT TO NOMINATIONS OF
DIRECTORS/TRUSTEES TO THE RESPECTIVE BOARDS

1.   The Fund's Governance Committee (the "Committee") will evaluate potential
     Board candidates to assess their qualifications. The Committee shall have
     the authority, upon approval of the Board, to retain an executive search
     firm to assist in this effort. The Committee may consider recommendations
     by business and personal contacts of current Board members and by executive
     search firms which the Committee may engage from time to time and may also
     consider shareholder recommendations. The Committee may consider the advice
     and recommendation of the Funds' investment manager and its affiliates in
     making the selection.

2.   The Committee shall screen candidates for Board membership. The Committee
     has not established specific qualifications that it believes must be met by
     a trustee nominee. In evaluating trustee nominees, the Committee considers,
     among other things, an individual's background, skills, and experience;
     whether the individual is an "interested person" as defined in the
     Investment Company Act of 1940; and

     whether the individual would be deemed an "audit committee financial
     expert" within the meaning of applicable SEC rules. The Committee also
     considers whether the individual's background, skills, and experience will
     complement the background, skills, and experience of other nominees and
     will contribute to the Board. There are no differences in the manner in
     which the Committee evaluates nominees for trustees based on whether the
     nominee is recommended by a shareholder.

3.   The Committee may consider nominations from shareholders for the Board at
     such times as the Committee meets to consider new nominees for the Board.
     The Committee shall have the sole discretion to determine the candidates to
     present to the Board and, in such cases where required, to shareholders.
     Recommendations for trustee nominees should, at a minimum, be accompanied
     by the following:

     -    the name, address, and business, educational, and/or other pertinent
          background of the person being recommended;

     -    a statement concerning whether the person is an "interested person" as
          defined in the Investment Company Act of 1940;

     -    any other information that the Funds would be required to include in a
          proxy statement concerning the person if he or she was nominated; and

     -    the name and address of the person submitting the recommendation and,
          if that person is a shareholder, the period for which that person held
          Fund shares.

     The recommendation also can include any additional information which the
     person submitting it believes would assist the Committee in evaluating the
     recommendation.

4.   Shareholders should note that a person who owns securities issued by
     Massachusetts Mutual Life Insurance Company (the parent company of the
     Funds' investment adviser) would be deemed an "interested person" under the
     Investment Company Act of 1940. In addition, certain other relationships
     with Massachusetts Mutual Life Insurance Company or its subsidiaries, with
     registered broker-dealers, or with the Funds' outside legal counsel may
     cause a person to be deemed an "interested person."

5.   Before the Committee decides to nominate an individual as a trustee,
     Committee members and other directors customarily interview the individual
     in person. In addition, the individual customarily is asked to complete a
     detailed questionnaire which is designed to elicit information which must
     be disclosed under SEC and stock exchange rules and to determine whether
     the individual is subject to any statutory disqualification from serving as
     a trustee of a registered investment company.



ITEM 11. CONTROLS AND PROCEDURES.

Based on their evaluation of the registrant's disclosure controls and procedures
(as defined in rule 30a-3(c) under the Investment Company Act of 1940 (17 CFR
270.30a-3(c)) as of 12/31/2008, the registrant's principal executive officer and
principal financial officer found the registrant's disclosure controls and
procedures to provide reasonable assurances that information required to be
disclosed by the registrant in the reports that it files under the Securities
Exchange Act of 1934 (a) is accumulated and communicated to registrant's
management, including its principal executive officer and principal financial
officer, to allow timely decisions regarding required disclosure, and (b) is
recorded, processed, summarized and reported, within the time periods specified
in the rules and forms adopted by the U.S. Securities and Exchange Commission.

There have been no changes in the registrant's internal controls over financial
reporting that occurred during the registrant's second fiscal quarter of the
period covered by this report that have materially affected, or are reasonably
likely to materially affect, the registrant's internal control over financial
reporting.

ITEM 12. EXHIBITS.

(a)  (1)  Not applicable to semiannual reports.

     (2)  Exhibits attached hereto.

     (3)  Not applicable.

(b)  Exhibit attached hereto.



                                   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.

Centennial Money Market Trust


By: /s/ John V. Murphy
    --------------------------------
    John V. Murphy
    Principal Executive Officer

Date: 02/11/2009

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


By: /s/ John V. Murphy
    --------------------------------
    John V. Murphy
    Principal Executive Officer

Date: 02/11/2009


By: /s/ Brian W. Wixted
    --------------------------------
    Brian W. Wixted
    Principal Financial Officer

Date: 02/11/2009