N-Q 1 e63286.htm

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

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number: 811-04919
______________________________________________

UBS Series Trust
______________________________________________________________________________
(Exact name of registrant as specified in charter)

51 West 52nd Street, New York, New York 10019-6114
______________________________________________________________________________
(Address of principal executive offices) (Zip code)

Mark F. Kemper, Esq.
UBS Global Asset Management
51 West 52nd Street
New York, NY 10019-6114
(Name and address of agent for service)
 
Copy to:
Jack W. Murphy, Esq.
Dechert LLP
1775 I Street, N.W.
Washington, DC 20006-2401

Registrant’s telephone number, including area code: 212-882 5000

Date of fiscal year end: December 31

Date of reporting period: March 31, 2008

Item 1. Schedule of Investments

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

Common stocks—69.54%          
    Number of    
Security description   shares   Value ($)
Air freight & couriers—1.92%          
FedEx Corp.   4,100     379,947
Ryder System, Inc.   3,100     188,821
          568,768
Airlines—0.49%          
Southwest Airlines Co.   11,700     145,080
Auto components—2.28%          
BorgWarner, Inc.   7,200     309,816
Johnson Controls, Inc.   10,800     365,040
          674,856
Banks—5.23%          
City National Corp.   1,500     74,190
Fifth Third Bancorp   12,200     255,224
SunTrust Banks, Inc.   3,700     204,018
The Bank of New York Mellon Corp.   8,800     367,224
Wells Fargo & Co.   22,200     646,020
          1,546,676
Beverages—0.50%          
Constellation Brands, Inc., Class A*   8,300     146,661
Biotechnology—1.59%          
Genzyme Corp.*   6,300     469,602
Building products—1.17%          
Masco Corp.   17,400     345,042
Computers & peripherals—0.95%          
Lexmark International, Inc., Class A*   2,300     70,656
NetApp, Inc.*   10,500     210,525
          281,181
Diversified financials—6.28%          
Citigroup, Inc.   27,600     591,192
Discover Financial Services   13,650     223,450
Federal Home Loan Mortgage Corp.   6,600     167,112
Morgan Stanley   11,600     530,120
Principal Financial Group, Inc.   6,200     345,464
          1,857,338
Diversified telecommunication services—1.76%          
AT&T, Inc.   6,100     233,630
Sprint Nextel Corp.   42,988     287,590
          521,220
Electric utilities—2.93%          
American Electric Power Co., Inc.   4,900     203,987
Exelon Corp.   7,000     568,890
Pepco Holdings, Inc.   3,800     93,936
          866,813

    Number of    
Security description   shares   Value ($)
Energy equipment & services—3.10%          
Baker Hughes, Inc.   4,600     315,100
ENSCO International, Inc.   1,500     93,930
Halliburton Co.   12,900     507,357
          916,387
Food & drug retailing—0.89%          
Sysco Corp.   9,100     264,082
Gas utilities—1.17%          
NiSource, Inc.   5,800     99,992
Sempra Energy   4,600     245,088
          345,080
Health care equipment & supplies—1.61%          
Covidien Ltd.   600     26,550
Medtronic, Inc.   6,200     299,894
Millipore Corp.*   2,200     148,302
          474,746
Health care providers & services—0.70%          
DaVita, Inc.*   1,900     90,744
UnitedHealth Group, Inc.   3,400     116,824
          207,568
Hotels, restaurants & leisure—1.93%          
Carnival Corp.   8,000     323,840
Royal Caribbean Cruises Ltd.   3,900     128,310
Starwood Hotels & Resorts Worldwide, Inc.   2,300     119,025
          571,175
Household durables—0.85%          
Fortune Brands, Inc.   3,600     250,200
Industrial conglomerates—2.59%          
General Electric Co.   20,700     766,107
Insurance—2.15%          
AFLAC, Inc.   5,700     370,215
Hartford Financial Services Group, Inc.   3,500     265,195
          635,410
Leisure equipment & products—0.30%          
Harley-Davidson, Inc.   2,400     90,000
Machinery—2.91%          
Illinois Tool Works, Inc.   9,100     438,893
PACCAR, Inc.   7,050     317,250
Pall Corp.   3,000     105,210
          861,353
Media—4.52%          
Comcast Corp., Class A*   25,500     493,170
Interpublic Group of Cos., Inc.*   25,400     213,614
News Corp., Class A   11,200     210,000

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

Common stocks—(concluded)        
    Number of     
Security description   shares Value ($)
Media—(concluded)        
Omnicom Group, Inc.   4,300   189,974
R.H. Donnelley Corp.*   5,220   26,413
Viacom, Inc., Class B*   5,100   202,062
        1,335,233
Metals & mining—1.28%        
Peabody Energy Corp.   7,400   377,400
Multi-line retail—0.07%        
Costco Wholesale Corp.   300   19,491
Oil & gas—2.07%        
Chevron Corp.   2,000   170,720
EOG Resources, Inc.   1,600   192,000
Marathon Oil Corp.   5,500   250,800
        613,520
Pharmaceuticals—7.55%        
Allergan, Inc.   6,400   360,896
Cephalon, Inc.*   1,400   90,160
Johnson & Johnson   6,600   428,142
Medco Health Solutions, Inc.*   5,600   245,224
Merck & Co., Inc.   8,600   326,370
Schering-Plough Corp.   10,200   146,982
Wyeth   15,200   634,752
        2,232,526
Road & rail—1.78%        
Burlington Northern Santa Fe Corp.   5,700   525,654
Semiconductor equipment & products—4.84%        
Analog Devices, Inc.   11,800   348,336
Intel Corp.   32,700   692,586
Linear Technology Corp.   5,400   165,726
Xilinx, Inc.   9,400   223,250
        1,429,898
Software—3.55%        
Intuit, Inc.*   5,700   153,957
Microsoft Corp.   18,400   522,192
Symantec Corp.*   22,563   374,997
        1,051,146
Specialty retail—0.17%        
Chico’s FAS, Inc.*   7,000   49,770
Textiles & apparel—0.41%        
Coach, Inc.*   4,000   120,600
Total common stocks (cost—$21,296,725)       20,560,583

    Face    
    amount ($)   Value ($)
US government obligations—4.39%          
US Treasury Bonds,          

4.750%, due 02/15/37

   45,000     48,400

8.125%, due 08/15/19

   100,000     139,305
US Treasury Inflation Index Bonds (TIPS),          

1.750%, due 01/15/28

   40,302     39,953
US Treasury Inflation Index Notes (TIPS),          

2.375%, due 04/15/11

   164,835     177,094
US Treasury Notes,          

3.625%, due 12/31/12

   175,000     184,393

4.625%, due 02/15/17

   645,000     708,441
Total US government obligations (cost—$1,286,809)   1,297,586
Mortgage & agency debt securities—7.18%          
Bear Stearns Adjustable Rate Mortgage Trust,          

Series 2005-1, Class 4A1,

          

5.353%, due 03/25/35

   53,128     47,597

Series 2007-3, Class 2A1,

          

5.640%, due 05/25/47

   94,528     86,756

Federal Home Loan Mortgage Corporation
Certificates,

    

2.875%, due 04/30/10

   100,000     101,117

3.500%, due 05/29/13

   105,000     105,696

4.500%, due 06/01/21

   98,282     97,885

5.600%, due 10/17/13

   100,000     101,465

Federal National Mortgage Association
Certificates ARM,

    

4.614%, due 09/01/35

   110,012     109,915

Federal National Mortgage Association
Certificates TBA,

    

5.000%, TBA

   65,000     64,330

Federal National Mortgage Association
Certificates,

          

2.500%, due 04/09/10

   60,000     60,238

5.000%, due 02/01/36

   42,151     41,780

5.500%, due 10/01/17

   87,130     89,431

6.000%, due 07/01/21

   57,659     59,403

6.000%, due 11/01/37

   72,983     74,830

6.000%, due 02/01/38

   75,000     76,898

6.070%, due 05/12/16

   105,000     105,401

6.500%, due 12/01/37

   196,593     203,777
FNMA REMIC, Series 2001-T4, Class A1,          

7.500%, due 07/25/41

   137,258     149,825

Government National Mortgage Assocation
Certificates TBA,

    

5.000%, TBA

   40,000     40,052

Government National Mortgage Assocation
Certificates,

          

6.500%, due 04/15/31

   90,548     94,679

JP Morgan Alternative Loan Trust,
Series 2006-A4, Class A7,

    

6.300%, due 09/25/36

   175,000     93,380

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

    Face    
    amount ($)   Value ($)
Mortgage & agency debt securities—(concluded)    

Merrill Lynch/Countrywide Commercial Mortgage Trust, Series 2007-8, Class C,

          

6.156%, due 08/12/491

   25,000     17,723
WAMU Mortgage Pass-Through Certificates,          

Series 2007-HY1, Class 3A3,

          

5.883%, due 02/25/371

   100,000     77,243

Series 2007-HY7, Class 2A2,

          

5.873%, due 07/25/371

   88,414     84,910
Wells Fargo Mortgage Backed Securities Trust,          

Series 2007-11, Class B1,

          

6.000%, due 08/25/37

   124,510     94,564

Series 2007-AR4, Class A1,

          

6.032%, due 08/25/37

   45,014     42,576

Total mortgage & agency debt securities (cost—$2,245,045)

   2,121,471
Commercial mortgage-backed securities—3.15%    
Banc of America Commercial Mortgage, Inc.,          

Series 2006-2, Class B,

          

5.775%, due 05/10/451

   25,000     18,269

Series 2006-5, Class B,

          

5.463%, due 09/10/47

   25,000     17,618

Series 2007-4, Class A4,

          

5.936%, due 02/10/511

   50,000     49,718
Citigroup Commercial Mortgage Trust,          

Series 2006-C4, Class A3,

          

5.725%, due 03/15/491

   50,000     50,463

Series 2006-C5, Class A4,

          

5.431%, due 10/15/49

   50,000     49,024

GE Capital Commercial Mortgage Corp.,
Series 2006-C1, Class A4,

          

5.340%, due 03/10/441

   75,000     74,177

GS Mortgage Securities Corp. II, Series 2006-RR2,
Class A1,

          

5.700%, due 06/23/461,2

   150,000     110,022

Hilton Hotel Pool Trust, Series 2000-HLTA,
Class A1,

          

7.055%, due 10/03/152

   185,925     196,945

JP Morgan Chase Commercial Mortgage
Securities Corp.,

          

Series 2005-LDP5, Class A4,

          

5.179%, due 12/15/441

   230,000     229,300

Series 2006-LDP8, Class A4,

          

5.399%, due 05/15/45

   75,000     73,455

Merrill Lynch Mortgage Trust,
Series 2007-C1, Class B,

          

6.022%, due 06/12/50

   25,000     18,460
Washington Mutual, Series 2002-AR17, Class 1A,          

5.526%, due 11/25/421

   46,658     44,296

Total commercial mortgage-backed securities
(cost—$971,050)

         931,747
Collateralized debt obligation—0.44%          
G-Force CDO Ltd., Series 2006-1A, Class A3,          

5.600%, due 09/27/463 (cost—$149,185)

   150,000     130,430
    Face    
    amount ($)   Value ($)
Asset-backed securities—1.20%          

American Home Mortgage Investment Trust,
Series 2006-3, Class 4A,
2.789%, due 11/25/351

   17,156     12,944

Daimler Chrysler Auto Trust,
Series 2007-A, Class A2B,

          

3.638%, due 03/08/111

   50,000     49,816

Fieldstone Mortgage Investment Corp.,
Series 2006-S1, Class A,

          

2.819%, due 01/25/371,2

   21,021     5,886

First Franklin Mortgage Loan Asset Backed Certificates, Series 2006-FFB, Class A2,
2.729%, due 12/25/261

   18,241     5,472

Greenpoint Home Equity Loan Trust,
Series 2004-3, Class A,
3.278%, due 03/15/351

   16,502     13,716
Home Equity Mortgage Trust          

Series 2006-3, Class A1,

          

5.472%, due 09/25/364

   11,600     5,336

Series 2006-5, Class A1,

          

5.500%, due 01/25/374

   46,153     17,077

Series 2006-6, Class 2A1,

          

2.699%, due 03/25/371,4

   16,375     5,240

Merrill Lynch First Franklin Mortgage Loan,
Series 2007-A, Class A1,

          

3.699%, due 10/25/271

   23,308     9,658

Merrill Lynch Mortgage Investors Trust,
Series 2006-SL1, Class A,

          

2.779%, due 09/25/361

   6,818     2,898

Morgan Stanley Mortgage Loan Trust,
Series 2006-14SL, Class A1,

          

2.759%, due 11/25/361

   17,351     9,543

Nomura Asset Acceptance Corp.,
Series 2006-S4, Class A1,

          

2.769%, due 08/25/361

   15,507     8,381

Pinnacle Capital Asset Trust,
Series 2006-A, Class B,

          

5.510%, due 09/25/092

   200,000     200,704
SACO I Trust, Series 2006-5, Class 2A1,          

2.749%, due 05/25/361

   21,745     7,747
Total asset-backed securities (cost—$467,247)         354,418
Corporate bonds—1.94%          
           
Automobile OEM—0.38%          
Ford Motor Credit Co.          

5.800%, due 01/12/09

   95,000     90,505
General Motors Acceptance Corp.          

6.875%, due 09/15/11

   30,000     22,961
          113,466
Banking-non-US—0.09%          
Royal Bank of Scotland Group PLC, Series 1          

9.118%, due 03/31/105

   25,000     25,220

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

    Face    
    amount ($)   Value ($)
Corporate bonds—(continued)          
           
Banking-US—0.10%          
Credit Suisse New York          

6.000%, due 02/15/18

   30,000     29,928
Brokerage—0.09%          
Bear Stearns Co., Inc.          

7.250%, due 02/01/18

   25,000     25,835
Chemicals—0.09%          
ICI Wilmington, Inc.          

4.375%, due 12/01/08

   25,000     25,130
Entertainment—0.10%          
Time Warner, Inc.          

6.875%, due 05/01/12

   30,000     30,970
Finance-noncaptive consumer—0.30%          
Countrywide Home Loan          

3.250%, due 05/21/08

   45,000     44,132
Residential Capital LLC          

3.490%, due 06/09/081

   25,000     19,750

6.375%, due 06/30/10

   50,000     25,125
          89,007
Finance-noncaptive diversified—0.11%          
General Electric Capital Corp.          

5.875%, due 01/14/38

   35,000     33,963
Food processors/beverage/bottling—0.13%          
SABMiller PLC          

6.500%, due 07/01/162

   35,000     37,943
Gas pipelines—0.11%          
Kinder Morgan Energy Partners          

5.800%, due 03/15/35

   40,000     33,833
Pharmaceuticals—0.14%          
Allergan, Inc.          

5.750%, due 04/01/16

   40,000     41,213
Real estate investment trust—0.11%          
ProLogis          

5.625%, due 11/15/15

   35,000     31,947
    Face    
    amount ($)   Value ($)
Corporate bonds—(concluded)          
           
Telecom-wirelines—0.19%          
Telecom Italia Capital          

5.250%, due 11/15/13

   60,000     56,063
Total corporate bonds (cost—$620,842)         574,518
    Number of      
    shares      
Investment companies6,* — 9.80%            
UBS High Yield Relationship Fund   69,369     1,459,364  
UBS U.S. Small Cap Equity Relationship Fund   35,984     1,439,021  
Total investment companies (cost—$2,598,784)         2,898,385  
    Face      
    amount ($)      
Repurchase agreement—2.75%            
Repurchase agreement dated 03/31/08 with State            

Street Bank & Trust Co., 0.750% due 04/01/08, collateralized by $57,069 US Treasury Bonds, 7.250% to 8.875% due 05/15/16 to 08/15/17 and $722,064 US Treasury Notes, 1.750% to 4.000% due 08/31/09 to 03/31/10; (value—$828,263); proceeds: $812,017
(cost—$812,000)

   812,000     812,000  

Investments of cash collateral from securities loaned—0.00%

      
    Number of         
    shares      
Money market funds7—0.00%            
DWS Money Market Series Institutional, 3.161%   89     89  
UBS Private Money Market Fund LLC,6 3.169%   1     1  

Total money market funds and investments of cash collateral from securities loaned (cost—$90)

         90  
Total investments (cost—$30,447,777)8,9—100.39%   29,681,228  
Liabilities in excess of other assets—(0.39)%         (114,343 )
Net assets—100.00%         29,566,885  

*   Non-income producing security.
     
1   Floating rate security. The interest rate shown is the current rate as of March 31, 2008.
     
2   Security exempt from registration under Rule 144A of the Securities Act of 1933. These securities, which represent 1.87% of net assets as of March 31, 2008, are considered liquid and may be resold in transactions exempt from registration, normally to qualified institutional buyers.
     
3   The security detailed in the table below, which represents 0.44% of net assets, is considered illiquid and restricted as of March 31, 2008:

                    Value at
            Acquisition cost       03/31/08 as
    Acquisition   Acquisition   as a percentage   Value   a percentage
Illiquid and restricted security   date   cost ($)   of net assets (%)   03/31/08 ($)   of net assets (%)
G-Force CDO Ltd., Series 2006-1A, Class A3, 5.600%, due 09/27/46   08/03/06   147,859   0.50   130,430   0.44

     
4   Step-up bond that converts to the noted fixed rate at a designated future date.
     
5   Perpetual bond security. The maturity date reflects the next call date.

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

6   The table below details the Portfolio’s transaction activity in affiliated issuers for the three months ended March 31, 2008.

                                      Net income
          Purchases   Sales   Net realized   Net unrealized       earned from
          during the   during the   gains for the   loss for the       affiliate for the
          three months   three months   three months   three months       three months
    Value at   ended   ended   ended   ended   Value at ended
Security description   12/31/07 ($)   03/31/08 ($)   03/31/08 ($)   03/31/08 ($)   03/31/08 ($)   03/31/08 ($) 03/31/08 ($)
UBS High Yield Relationship Fund   1,820,470     -     300,000     55,399     (116,505 )   1,459,364   -  
UBS Private Money Market Fund LLC   2     -     1     -     -     1   -  
UBS U.S. Small Cap Equity Relationship Fund   1,684,579     -     -     -     (245,558 )   1,439,021   -  

7   Rates shown reflect yield at March 31, 2008.
     
8   Cost of investments shown approximates cost for federal income tax purposes. Gross unrealized appreciation of investments and gross unrealized depreciation of investments at March 31, 2008 were $1,978,857 and $2,745,406, respectively, resulting in net unrealized depreciation of investments of $766,549.
     
9   The Portfolio calculates net asset values based on the current market value for its portfolio securities. The Portfolio normally obtains market values for its securities from independent pricing sources. Independent pricing sources may use last reported sale prices, current market quotations or valuations from computerized “matrix” systems that derive values based on comparable securities. Securities traded in the over-the-counter (“OTC”) market and listed on The Nasdaq Stock Market, Inc. (“NASDAQ”) normally are valued at the NASDAQ Official Closing Price. Other OTC securities are valued at the last bid price available prior to valuation. Securities which are listed on US and foreign stock exchanges normally are valued at the last sale price on the day the securities are valued or, lacking any sales on such day, at the last available bid price. In cases where securities are traded on more than one exchange, the securities are valued on the exchange designated as the primary market by UBS Global Asset Management (Americas) Inc. If a market value is not available from an independent pricing source for a particular security, that security is valued at fair value as determined in good faith by or under the direction of the Trust’s Board of Trustees (the “Board”). Various factors may be reviewed in order to make a good faith determination of a security’s fair value. These factors may include, but are not limited to, the type and cost of the security; contractual or legal restrictions on resale of the security; relevant financial or business developments of the issuer; the value of actively traded similar or related securities; conversion or exchange rights on the security; related corporate actions; and changes in overall market conditions. If events occur that materially affect the value of securities (particularly non-US securities) between the close of trading in those securities and the close of regular trading on the New York Stock Exchange, these securities would be fair valued. The amortized cost method of valuation, which approximates market value, generally is used to value short-term debt-instruments with sixty days or less remaining to maturity, unless the Board determines that this does not represent fair value.

In September 2006, the Financial Accounting Standards Board released Statement of Financial Accounting Standards No. 157 (“FAS 157”). FAS 157 requires disclosure surrounding the various inputs that are used in determining the value of the Fund’s investments. These inputs are summarized into the three broad levels listed below:

Level 1 – quoted prices in active markets for identical securities.
Level 2 – other significant observable inputs, including, but not limited to, quoted prices for similar securities, interest rates, prepayment speeds and credit risks.
Level 3 – significant unobservable inputs inclusive of the Portfolio’s own assumptions in determining the fair value of investments.

    The following is a summary of the inputs used as of March 31, 2008 in valuing the Portfolio’s assets:

        Measurements at 03/31/08
        Quoted prices in            
        active markets for   Significant other   Significant
        identical assets   observable inputs   unobservable
Description   Total ($)   (Level 1) ($)   (Level 2) ($)   inputs (Level 3) ($)
Assets                      
Securities   29,681,228   22,332,087     7,212,825     136,316  

The following is a rollforward of the Portfolio’s assets that were valued using unobservable inputs for the period:

  Measurements using
  unobservable inputs (Level 3)
       
    Securities  
Assets      
Beginning balance   -  
Accrued discounts/(premiums)   312  
Total gains or losses (realized/unrealized) included in earnings   (11,564 )
Purchases, sales, issuances and settlements (net)   (440 )
Transfers in and/or out of Level 3   148,008  
Ending balance   136,316  
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at 03/31/08   6  

ARM   Adjustable Rate Mortgage. The interest rate shown is the current rates as of March 31, 2008.
     
CDO   Collateralized Debt Obligation
     
FNMA   Federal National Mortgage Association
     
GS   Goldman Sachs
     
OEM   Original Equipment Manufacturer
     
REMIC   Real Estate Mortgage Investment Conduit

UBS Series Trust - U.S. Allocation Portfolio
Schedule of investments – March 31, 2008 (unaudited)

TBA   (To Be Announced) Securities are purchased on a forward commitment basis with an approximate principal amount (generally +/- 1.0%) and no definite maturity date. The actual principal amount and maturity date will be determined upon settlement when the specific mortgage pools are assigned.
     
TIPS   Treasury inflation protected securities (“TIPS”) are debt securities issued by the US Treasury whose principal and/or interest payments are adjusted for inflation, unlike debt securities that make fixed principal and interest payments. The interest rate paid by the TIPS is fixed, while the principal value rises or falls based on changes in a published Consumer Price Index (“CPI”). Thus, if inflation occurs, the principal and interest payments on the TIPS are adjusted accordingly to protect investors from inflationary loss. During a deflationary period, the principal and interest payments decrease, although the TIPS principal amounts will not drop below their face amounts at maturity. In exchange for the inflation protection, the TIPS generally pay lower interest rates that typical US Treasury securities. Only if inflation occurs would TIPS be expected to offer a higher real yield than a conventional Treasury bond of the same maturity.
     
WAMU   Washington Mutual

Issuer breakdown by country of origin

Percentage of total investments (%)
United States   97.6
Panama   1.1
Cayman Islands   0.4
Liberia   0.4
United Kingdom   0.2
Italy   0.2
Bermuda   0.1
Total   100.0

For more information regarding the Portfolio’s other significant accounting policies, please refer to the Portfolio’s annual report to shareholders dated December 31, 2007.


Item 2. Controls and Procedures.

(a)  
The registrant’s principal executive officer and principal financial officer have concluded that the registrant’s disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (“Investment Company Act”)) are effective based on their evaluation of these controls and procedures as of a date within 90 days of the filing date of this document.
     
(b)  
The registrant’s principal executive officer and principal financial officer are aware of no changes in the registrant’s internal control over financial reporting (as defined in Rule 30a-3(d) under the Investment Company Act) that occurred during the registrant’s last fiscal quarter that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 3. Exhibits.

(a)  
Certifications of principal executive officer and principal financial officer of registrant pursuant to Rule 30a-2(a) under the Investment Company Act is attached hereto as Exhibit 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.

UBS Series Trust

By:   /s/ Kai R. Sotorp
    Kai R. Sotorp
    President
     
Date:   May 30, 2008

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/ Kai R. Sotorp
    Kai R. Sotorp
    President
     
Date:   May 30, 2008
     
By:   /s/ Thomas Disbrow
    Thomas Disbrow
    Vice President and Treasurer
     
Date:   May 30, 2008