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                                                                    EXHIBIT 10.1

                              KILROY REALTY, L.P.
                 FIRST AMENDMENT TO THIRD AMENDED AND RESTATED
                        AGREEMENT OF LIMITED PARTNERSHIP

          THIS FIRST AMENDMENT TO THIRD AMENDED AND RESTATED AGREEMENT OF
LIMITED PARTNERSHIP (this "Amendment") is made as of October 2, 1998 by Kilroy
Realty Corporation, a Maryland corporation, as general partner (the "General
Partner") of Kilroy Realty, L.P., a Delaware limited partnership (the
"Partnership"), for the purpose of amending the Third Amended and Restated
Agreement of Limited Partnership, dated as of April 17, 1998, as amended to the
date hereof (the "Partnership Agreement").

          WHEREAS, the General Partner has entered into a Rights Agreement,
dated as of October 2, 1998 (the "Rights Agreement"), pursuant to which the
General Partner will distribute to holders of the General Partner's common stock
rights to purchase shares of a newly authorized class of preferred stock (the
"Rights Plan"); and

          WHEREAS, in connection with the adoption of the Rights Plan, it is
necessary to amend the Partnership Agreement to provide for the equitable
treatment of Limited Partners under the terms of the Partnership Agreement,
including, without limitation, in connection with the Limited Partners' right of
redemption under Section 8.6 of the Partnership Agreement; and

          WHEREAS, pursuant to Section 7.3.E(3) of the Partnership Agreement,
the General Partner may, without the Consent of the Limited Partners (as such
term is defined in the Partnership Agreement) amend the Partnership Agreement to
reflect a change that is of an inconsequential nature and does not adversely
affect the Limited Partners in any material respect, or to cure any ambiguity
in, correct or supplement any provision in, or make other changes with respect
to matters arising under, the Partnership Agreement that will not be
inconsistent with law or with the provisions of the Partnership Agreement; and

          WHEREAS, the General Partner believes that none of the actions taken
pursuant to this Amendment adversely affect the Limited Partners in any material
respect or are inconsistent with law or with the provisions of the Partnership
Agreement; and

          WHEREAS, the General Partner and the Partnership believe it is
desirable and in the best interest of the Partnership to amend the Partnership
Agreement as set forth herein.

          NOW THEREFORE, in consideration of the premises set forth above, the
General Partner, on behalf of itself and the Limited Partners, undertakes to
implement the following amendments to the Partnership Agreement:

          Section 1.  Defined Terms.  Capitalized terms used without definition
                      -------------                                            
in this Amendment shall have the meaning given to each such term in the
Partnership Agreement.

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          Section 2.  Amendments.
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          (a)  Section 1.1.
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               (1) Deemed Value of the Partnership Interests.  The definition of
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     "Deemed Value of the Partnership Interests" set forth in Section 1.1 of the
     Partnership Agreement is hereby deleted in its entirety and replaced with
     the following:

          "Deemed Value of the Partnership Interests" means, as of any date with
           -----------------------------------------                            
          respect to any class or series of Partnership Interests (i) the total
          number of Partnership Units of the General Partner in such class of
          Partnership Interests (as provided for in Sections 4.1 and 4.3.C)
          issued and outstanding as of the close of business on such date
          multiplied by the sum of (x) the Fair Market Value of the number of
          shares of capital stock of the General Partner which corresponds to
          one Partnership Unit such class or series of Partnership Interests on
          such date (as adjusted pursuant to Section 7.5 (in the event the
          General Partner acquires material assets, other than on behalf of the
          Partnership) and for stock dividends and distributions, stock splits
          and subdivisions, reverse stock splits and combinations, distributions
          of rights, warrants or options, and distributions of evidences of
          indebtedness or assets relating to assets not received by the General
          Partner pursuant to a pro rata distribution by the Partnership);
                                --- ----                                  
          divided by (ii) the Percentage Interest of the General Partner in such
          ------- --                                                            
          class or series of Partnership Interests on such date; provided, that,
                                                                 --------       
          if no outstanding shares of capital stock of the General Partner
          correspond to a class of series of Partnership Interests, the Deemed
          Value of Partnership Interests with respect to such class or series
          shall be equal to an amount reasonably determined by the General
          Partner.  Without limiting the generality of the foregoing, the Deemed
          Value of the Partnership Interests referenced in the preceding
          sentence shall be adjusted for the issuance, distribution and
          triggering of exercisability of the Rights (which adjustment shall be
          made as necessary to equitably reflect the dilution in REIT Shares
          resulting from the issuance and exercise of the Rights, in each case
          taking into account any increase pursuant to Section 4.5.B in the
          number of Partnership Units held by the Limited Partners).

               (2) REIT Shares Amount.  The definition of "REIT Shares Amount"
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     set forth in Section 1.1 of the Partnership Agreement is hereby deleted in
     its entirety and replaced with the following:

          "REIT Shares Amount" means, as of any date, an aggregate number of
           ------------------                                               
          REIT Shares equal to the number of Tendered Units, or in the case of
          Section 11.2.B, all Units, as adjusted pursuant to Section 7.5 (in the
          event the General Partner acquires material assets, other than on
          behalf of the Partnership) and for stock dividends and distributions,
          stock splits and

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          subdivisions, reverse stock splits and combinations, distributions of
          rights, warrants or options, and distributions of evidences of
          indebtedness or assets relating to assets not received by the General
          Partner pursuant to a pro rata distribution by the Partnership.
                                --- ----
          Without limiting the generality of the foregoing, such aggregate
          number of REIT Shares referenced in the preceding sentence shall be
          adjusted for the issuance, distribution and triggering of
          exercisability of the Rights governed by the Rights Agreement (which
          adjustment shall be satisfied by issuing together with the REIT Shares
          Amount the aggregate number Rights (if prior to expiration of the
          Rights pursuant to the Rights Agreement) or REIT Shares (if subsequent
          to the triggering of the exercisability of such Rights and subsequent
          to the expiration of the Rights pursuant to the Rights Agreement)
          necessary to reflect equitably the dilution in REIT Shares resulting
          from the issuance and exercise of the Rights, in each case taking into
          account any increase pursuant to Section 4.5.B in the number of
          Partnership Units held by the Limited Partners).

               (3) Fair Market Value.  The definition of "Fair Market Value" set
                   -----------------                                            
     forth in Section 1.1 of the Partnership Agreement is hereby deleted in its
     entirety and replaced with the following:

          "Fair Market Value" means, with respect to any security of the General
           -----------------                                                    
          Partner, the average of the daily market price for the ten (10)
          consecutive trading days immediately preceding the date with respect
          to which "Fair Market Value" must be determined hereunder or, if such
          date is not a Business Day, the immediately preceding Business Day.
          The market price for each such trading day shall be:  (i) if such
          security is listed or admitted to trading on any securities exchange
          or the Nasdaq National Market, the closing price, regular way, on such
          day, or if no such sale takes place on such day, the average of the
          closing bid and asked prices on such day, (ii) if such security is not
          listed or admitted to trading on any securities exchange or the Nasdaq
          National Market, the last reported sale price on such day or, if no
          sale takes place on such day, the average of the closing bid and asked
          prices on such day, as reported by a reliable quotation source
          designated by the General Partner, or (iii) if such security is not
          listed or admitted to trading on any securities exchange or the Nasdaq
          National Market and no such last reported sale price or closing bid
          and asked prices are available, the average of the reported high bid
          and low asked prices on such day, as reported by a reliable quotation
          source designated by the General Partner, or if there shall be no bid
          and asked prices on such  day, the average of the high bid and low
          asked prices, as so reported, on the most recent day (not more than 10
          days prior to the date in question) for which prices have been so
          reported; provided, that if there are no bid and asked prices reported
                    --------                                                    
          during the 10 days prior to the date in

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          question, the Fair Market Value of such security shall be determined
          by the General Partner acting in good faith on the basis of such
          quotations and other information as it considers, in its reasonable
          judgment, appropriate. In the event the REIT Shares Amount for shares
          of common stock includes rights that a holder of such shares would be
          entitled to receive, then the Fair Market Value of such rights shall
          be determined by the General Partner acting in good faith on the basis
          of such quotations and other information as it considers, in its
          reasonable judgment, appropriate; provided, that in connection with
                                            --------
          determining the Deemed Value of the Partnership Interests for purposes
          of determining the number of additional Partnership Units issuable
          upon a Capital Contribution funded by an underwritten public offering
          of shares of capital stock of the General Partner, the Fair Market
          Value of such shares shall be the public offering price per share of
          such class of capital stock sold; and, provided further, that the Fair
                                                 -------- -------
          Market Value of any rights issued pursuant to the Rights Agreement
          shall be deemed to have no value unless a "triggering event" (as
          defined in the Rights Agreement) shall have occured (i.e., if the
          Rights issued pursuant thereto are no longer "attached" to the REIT
          Shares and are able to trade independently).

               (4) Rights and Rights Agreement. The definition of "Rights" and
                   ---------------------------
     "Rights Agreement" set forth below is hereby added to Section 1.1 of the
     Partnership Agreement between the defined terms "REIT Shares Amount" and
     "Securities Act":

          "Rights" means the rights issued pursuant to the Rights Agreement.
           ------                                                           

          "Rights Agreement" means the Rights Agreement, dated as of October 2,
           ----------------                                                    
          1998, by and between the General Partner and ChaseMellon Shareholder
          Services, L.L.C.

          (b) Section 4.5.  The Partnership Agreement is hereby amended by
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renaming Section 4.5 as 4.5.A and adding the following as new Section 4.5.B.

               B.  Notwithstanding the foregoing provisions of this Article IV,
     in the event the General Partner has made contributions of cash to the
     Partnership attributable to the General Partner's receipt of cash pursuant
     to the exercise of the Rights, the General Partner shall be issued a number
     of Partnership Units as a result of such contribution equal to the number
     of REIT Shares sold pursuant to such exercise.  In such case or in the
     event the General Partner makes other contributions to the Partnership in
     connection with the issuance of REIT Shares after the Rights have become
     excercisable, the number of Partnership Units held by the Limited Partners
     shall be increased to equitably offset the dilution resulting from such
     issuance.

          Section 3.  Miscellaneous.
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          (a) Effect of Amendment.  Except as specifically modified hereby, all
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terms and provisions of the Partnership Agreement shall continue to remain in
full force and effect and, except as the context otherwise requires, each
reference to the Partnership Agreement in this Amendment shall be a reference to
the Partnership Agreement as amended hereby.

          (b) Counterparts.  This Amendment may be executed in two or more
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counterparts, each of which when and as executed shall be deemed to be an
original, and all of which when taken together shall constitute one and the same
instrument.

          (c) Successors and Assigns.  This Amendment shall inure to the benefit
              ----------------------                                            
of and be binding upon the successors and assigns of each of the Partners.

          (e) Headings.  The headings in this Amendment are for convenience of
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reference only and shall not limit or otherwise affect the meaning hereof.

          (f) Governing Law.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
              -------------                                                    
IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF DELAWARE.

          (g) Severability.  In the event that any one or more of the provisions
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contained herein, or the application thereof in any circumstances, is held
invalid, illegal or unenforceable in any respect for any reason, the validity,
legality and enforceability of any such provision in every other respect and of
the remaining provisions hereof shall not be in any way impaired or affected, it
being intended that each party's rights and privileges shall be enforceable to
the fullest extent permitted by law.


                           (Signature Page Follows.)

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          IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the date first written above.

                                       GENERAL PARTNER
                                       ---------------

                                       KILROY REALTY CORPORATION
 

                                       By: /s/ Jeffrey C. Hawken
                                          ----------------------------
                                          Jeffrey C. Hawken
                                          Executive Vice President and  
                                          Chief Operating Officer

                                      S-1
