EXHIBIT 8.1

Opinion of Latham & Watkins

February 21, 2002

KILROY REALTY CORPORATION

2250 East Imperial Highway, Suite 1200

El Segundo, California 90245

Re:    Registration Statement on Form S-3

Ladies and Gentlemen:

We have acted as tax counsel to Kilroy Realty Corporation, a Maryland corporation (the “Company”), in connection with its registration of 1,133 shares of common stock of the Company pursuant to the registration statement filed with the Securities and Exchange Commission (the “Commission”) on Form S-3 on February 21, 2002, as amended (together with all exhibits thereto and documents incorporated by reference therein, the “Registration Statement”).

You have requested our opinion concerning the statements in the Registration Statement under the caption “Material Federal Income Tax Considerations.” This opinion is based on various factual assumptions, including the facts set forth in the Registration Statement concerning the business, properties and governing documents of the Company, Kilroy Realty, L.P., (the “Operating Partnership”) and their subsidiaries. We have also been furnished with, and with your consent have relied upon, certain representations made by the Company, the Operating Partnership and their subsidiaries with respect to certain factual matters through a certificate of an officer of the Company (the “Officer’s Certificate”). With respect to matters of Maryland law, we have relied upon the opinion of Ballard Spahr Andrews & Ingersoll, LLP, counsel for the Company, dated February 20, 2002.

In our capacity as tax counsel to the Company, we have made such legal and factual examinations and inquiries, including an examination of originals or copies certified or otherwise identified to our satisfaction of such documents, corporate records and other instruments as we have deemed necessary or appropriate for purposes of this opinion. For the purposes of our opinion, we have not made an independent investigation or audit of the facts set forth in the above referenced documents or in the Officer’s Certificate. In addition, in rendering this opinion we have assumed the truth and accuracy of all representations and statements made to us which are qualified as to knowledge or belief, without regard to such qualification. In our examination, we have assumed the authenticity of all documents submitted to us as originals, the genuineness of all signatures thereon, the legal capacity of natural persons executing such documents and the conformity to authentic original documents of all documents submitted to us as copies.

We are opining herein as to the effect on the subject transaction only of the federal income tax laws of the United States and we express no opinion with respect to the applicability thereto, or the effect thereon, of other federal laws, the laws of any state or other

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February 21, 2002

Page 2

jurisdiction or as to any matters of municipal law or the laws of any other local agencies within any state.

Based on such facts, assumptions, and representations, it is our opinion that the statements in the Registration Statement set forth under the caption “Material Federal Income Tax Considerations,” insofar as they purport to describe or summarize certain provisions of the agreements, statutes or regulations referred to therein, are accurate descriptions or summaries in all material respects.

No opinion is expressed as to any matter not discussed herein.

This opinion is rendered to you as of the date of this letter, and we undertake no obligation to update this opinion subsequent to the date hereof. This opinion is based on various statutory provisions, regulations promulgated thereunder and interpretations thereof by the Internal Revenue Service and the courts having jurisdiction over such matters, all of which are subject to change either prospectively or retroactively. Also, any variation or difference in the facts from those set forth in the Registration Statement or the Officer’s Certificate may affect the conclusions stated herein. Moreover, the Company’s qualification and taxation as a real estate investment trust depends upon the Company’s ability to meet, through actual annual operating results, asset composition, distribution levels and diversity of stock ownership, the various qualification tests imposed under the Internal Revenue Code, the results of which have not been and will not be reviewed by Latham & Watkins. Accordingly, no assurance can be given that the actual results of the Company’s operations for any one taxable year will satisfy such requirements.

This opinion is rendered only to you, and is solely for your benefit in connection with the Registration Statement. We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the use of our name under the captions “Material Federal Income Tax Considerations” and “Legal Matters” in the Registration Statement. In giving this consent, we do not hereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act of 1933 or the rules or regulations of the Commission promulgated thereunder. This opinion may not be relied upon by you for any other purpose, or furnished to, quoted to, or relied upon by any other person, firm, or corporation, for any purpose, without our prior written consent.

Ve ry truly yours,

/s/     Latham & Watkins