Exhibit 10.25


                             PS BUSINESS PARKS, L.P.

                        AMENDMENT TO AGREEMENT OF LIMITED
                             PARTNERSHIP RELATING TO
                ADDITIONAL 8 7/8% SERIES X CUMULATIVE REDEEMABLE
                                 PREFERRED UNITS

     This  Amendment  to the  Agreement  of Limited  Partnership  of PS Business
Parks, L.P. a California limited  partnership (the  "Partnership"),  dated as of
the 23rd day of  September,  1999 (this  "Amendment")  amends the  Agreement  of
Limited Partnership of the Partnership,  dated as of March 17, 1998 by and among
PS Business Parks, Inc. (the "General Partner") and each of the limited partners
executing a signature page thereto, as amended  (collectively,  the "Partnership
Agreement").  Capitalized terms used herein and not otherwise defined shall have
the  meanings  ascribed  to such  terms in the  Partnership  Agreement.  Section
references  are  (unless  otherwise  specified)  references  to sections in this
Amendment.

     WHEREAS,  pursuant  to Section  4.2(a) of the  Partnership  Agreement,  the
General  Partner  caused the  Partnership  to issue  1,200,000  8 7/8%  Series X
Cumulative  Redeemable  Preferred  Units  pursuant to that certain  Amendment to
Agreement  of  Limited  Partnership  Relating  to 8  7/8%  Series  X  Cumulative
Redeemable  Preferred  Units,  dated September 7, 1999 (the "Prior  Amendment"),
with the  designations,  preferences  and relative,  participating,  optional or
other special rights, powers and duties set forth therein;

     WHEREAS,  pursuant  to  Section  4.2(a) of the  Partnership  Agreement  the
General Partner desires to cause the  Partnership to issue  additional  Series X
Cumulative Redeemable Preferred Units, with the same designations, prefererences
and relative, participating, optional or other special rights, powers and duties
of the Series X Preferred Units set forth in the Prior Amendment;

     WHEREAS,  pursuant  to Section  4.2(a) of the  Partnership  Agreement,  the
General  Partner,  without the consent of the  Limited  Partners,  may amend the
Partnership  Agreement by executing a written instrument setting forth the terms
of such amendment; and

     WHEREAS,  the General  Partner  desires by this  Amendment  to so amend the
Partnership  Agreement  as of the date first set forth  above to provide for the
and issuance of additional Series X Preferred Units.

     NOW, THEREFORE, the Partnership Agreement is hereby amended as follows:

     Section 1.  Definitions.  Capitalized  terms not otherwise  defined  herein
shall have their respective meanings set forth in the Partnership  Agreement and
the Prior  Amendment.  For purposes of this Amendment,  Series X Preferred Units
shall mean those certain 8 7/8% Series X Cumulative  Redeemable  Preferred Units
issued on  September  7,  1999  together  with the  additional  8 7/8%  Series X
Cumulative Redeemable Preferred Units issued as of the date hereof.

     Section 2.  Number of Series X  Preferred  Units.  The  Partnership  hereby
increases  the number of Series X Preferred  Units by 400,000 (the "New Units"),
thereby  causing the total  number of Series X Preferred  Units to be  1,600,000
(the "Increased Series X Preferred Units"). All terms and conditions established
in the Prior  Amendment  relating  to the  Series X  Preferred  Units are hereby
ratified  and  confirmed  and shall  apply to the  Increased  Series X Preferred
Units.  Notwithstanding the foregoing or anything contained herein, the Priority
Return  distributions  relating to the New Units shall  accrue from the original
date of issuance of the New Units.

     Section 3. Exhibit A to Partnership Agreement. In order to duly reflect the
issuance of the New Units  provided  for herein,  the  Partnership  Agreement is
hereby further  amended  pursuant to Section 12.3 thereof by deleting  Exhibit A
thereto and replacing Exhibit A attached hereto therefor.

     Section 4. Inconsistent  Provisions.  Nothing to the contrary  contained in
the Partnership Agreement shall limit any of the rights or obligations set forth
in this Amendment.




     IN WITNESS  WHEREOF this  Amendment  has been executed as of the date first
above written.


                                           PS BUSINESS PARKS, INC.

                                           By: /s/ Jack Corrigan
                                               -------------------------
                                               Jack Corrigan
                                               Vice President and
                                               Chief Financial Officer