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                                                                     EXHIBIT 8.1






                                                                    June 6, 2001



SL Green Realty Corp.
420 Lexington Avenue
New York, New York  10170

Ladies and Gentlemen:

      You have requested our opinion concerning certain of the federal income
tax matters with respect to SL Green Realty Corp. (the "Company") in connection
with the Form S-3 Registration Statement of the Company to be filed by the
Company with the Securities and Exchange Commission (the "SEC") on June 6, 2001
(the "Registration Statement").

      This opinion is based, in part, upon various assumptions and factual
representations set forth in the Registration Statement, in registration
statements on Forms S-11 and S-3 previously filed by the Company with the SEC
and in a letter delivered to us by the Company today. This opinion is also based
upon the Internal Revenue Code of 1986, as amended (the "Code"), the Treasury
Regulations promulgated thereunder and existing administrative and judicial
interpretations thereof, all as they exist at the date of this letter. All of
the foregoing statutes, regulations and interpretations are subject to change,
in some circumstances with retroactive effect. Any changes to the foregoing
authorities might result in modifications of our opinions contained herein.

      Based on the foregoing, we are of the opinion that, commencing with the
Company's taxable year ended December 31, 1997, the Company was organized in
conformity with the requirements for qualification and taxation as a real estate
investment trust (a "REIT") under the Code and the proposed method of operation
of the Company will enable the Company to meet the requirements for
qualification and taxation as a REIT.

      We express no opinion with respect to the transactions described herein
and in the Registration Statement other than those expressly set forth herein.
Furthermore, the Company's qualification as a REIT will depend on the Company's
meeting, in its actual operations, the applicable asset composition, source of
income, shareholder diversification, distribution and

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other requirements of the Code and Treasury Regulations necessary for a
corporation to qualify as a REIT. We will not review these operations and no
assurance can be given that the actual operations of the Company and its
affiliates will meet these requirements or the representations made to us with
respect thereto.

      This opinion is furnished to you for your use in connection with the
Registration Statement. We hereby consent to the filing of this opinion as
Exhibit 8.1 to the Registration Statement and to the use of our name in
connection with the material discussed therein under the caption "Material
Federal Income Tax Consequences."

                                 Very truly yours,
                                  /S/
                                 Sidley Austin Brown & Wood LLP








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