Exhibit 5.1

               [LETTERHEAD OF BALLARD SPAHR ANDREWS & INGERSOLL]

                               December 23, 1997



Kilroy Realty Corporation
2250 East Imperial Highway
El Segundo, California 90245

     Re:  Kilroy Realty Corporation, a Maryland corporation, (the "Company") -
          Registration Statement on Form S-8 (the "Registration Statement")
          pertaining to One Million Five Hundred Thousand (1,500,000) shares
          (the "Plan Shares") of common stock, par value one cent ($.01) per
          share ("Common Stock"), to be issued pursuant to the 1997 Stock Option
          and Incentive Plan for Key Employees of the Company, Kilroy Realty,
          L.P. and Kilroy Services, Inc. (the "Plan")
          ----------------------------------------------------------------------

Ladies and Gentlemen:

     In connection with the registration of the Plan Shares under the Securities
Act of 1933, as amended (the "Act") by the Company on Form S-8 to be filed with
the Securities and Exchange Commission on or about December 23, 1997, (the
"Registration Statement"), you have requested our opinion with respect to the
matters set forth below.

     We have acted as special Maryland corporate counsel for the Company in
connection with the matters described herein.  In our capacity as special
Maryland corporate counsel to the Company, we have reviewed and are familiar
with proceedings taken and proposed to be taken by the Company in connection
with the authorization, issuance and sale of the Plan Shares, and for purposes
of this opinion have assumed such proceedings will be timely completed in the
manner presently proposed.  In addition, we have relied upon certificates and
advice from the officers of the Company upon which



 
BALLARD SPAHR ANDREWS & INGERSOLL

Kilroy Realty Corporation
December 23, 1997
Page 2

we believe we are justified in relying and on various certificates from, and
documents recorded with, the State Department of Assessments and Taxation of
Maryland (the "SDAT"), including the charter of the Company (the "Charter"),
consisting of Articles of Incorporation filed with the SDAT on September 13,
1996 and Articles of Amendment and Restatement filed with the SDAT on January
21, 1997.  We have also examined the Amended and Restated Bylaws of the Company,
adopted as of January 26, 1997, (the "Bylaws"), resolutions of the Board of
Directors of the Company adopted on December 8, 1996 and January 27, 1997 and in
full force and effect on the date hereof, the Plan, and such other laws,
records, documents, certificates, opinions and instruments as we have deemed
necessary to render this opinion.

     We have assumed the genuineness of all signatures and the authenticity of
all documents submitted to us as originals and the conformity to the originals
of all documents submitted to us as certified, photostatic or conformed copies.
In addition, we have assumed that each person executing any instrument, document
or certificate referred to herein on behalf of any party is duly authorized to
do so.  We have also assumed that none of the Plan Shares have been or will be
issued or transferred in violation of the restrictions on ownership and transfer
of stock contained in the Charter of the Company under the caption "Restrictions
on Ownership and Transfer to Preserve Tax Benefits".

     Based on the foregoing, and subject to the assumptions and qualifications
set forth herein, it is our opinion that, as of the date of this letter: (i) the
Plan Shares have been duly reserved and duly authorized for issuance by the
Company as direct stock awards or upon the exercise of options granted under the
Plan, and when such Plan Shares are issued and delivered by the Company as
direct stock awards or upon the exercise of options granted under the Plan and
the consideration for such Plan Shares has been received in full by the Company,
all in accordance with the Plan and any such options, such Plan Shares will be
validly issued, fully paid and non-assessable; and (ii) of the Plan Shares,
100,000 shares have been issued to Richard E. Moran, Jr. (the "Moran Shares"),
and the Moran Shares are validly issued, fully paid and non-assessable.

     We consent to your filing this opinion as an exhibit to the Registration
Statement, and further consent to the filing of this opinion as an exhibit to
the applications to securities commissioners for the various states of the
United States for registration of the Shares.  We also consent to the
identification of our firm as Maryland counsel to the Company in the section of



 
BALLARD SPAHR ANDREWS & INGERSOLL

Kilroy Realty Corporation
December 23, 1997
Page 3


the Prospectus (which is part of the Registration Statement) entitled "Legal
Matters."

     The opinions expressed herein are limited to the laws of the State of
Maryland and we express no opinion concerning any laws other than the laws of
the State of Maryland.  Furthermore, the opinions presented in this letter are
limited to the matters specifically set forth herein and no other opinion shall
be inferred beyond the matters expressly stated.

                                    Very truly yours,

                                    /s/ Ballard Spahr Andrews & Ingersoll