Exhibit 5.1

[Goodwin Procter LLP Letterhead]

Boston Properties, Inc.

The Prudential Center

800 Boylston Street, Suite 1900

Boston, MA 02199-8103

Ladies and Gentlemen:

This opinion letter is furnished to you in our capacity as counsel for Boston Properties, Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-3 (as amended or supplemented, the “Registration Statement”) filed by the Company with the United States Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), and the prospectus supplement, dated April 1, 2011 (the “Prospectus Supplement”), filed by the Company with the Commission pursuant to Rule 424(b) under the Securities Act relating to the offering of 5,906 shares (the “Shares”) of common stock, par value $0.01 per share. The Shares may be issued from time to time by the Company to the extent that the holder of 5,906 common units of limited partnership interest (the “OP Units”) in Boston Properties Limited Partnership, a Delaware limited partnership (the “Operating Partnership”), in accordance with the terms of the Second Amended and Restated Agreement of Limited Partnership of Boston Properties Limited Partnership, dated as of June 29, 1998, as amended (the “Partnership Agreement”), tenders the OP Units to the Operating Partnership for redemption and the Company exercises its contractual right to acquire such tendered OP Units in exchange for the Shares.

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions expressed below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinions set forth below, on certificates of officers of the Company.

The opinion expressed below is limited to the Delaware General Corporation Law (which includes reported judicial decisions interpreting the Delaware General Corporation Law).

For purposes of the opinion expressed below, we have assumed that a sufficient number of authorized but unissued shares of the Company’s Common Stock will be available for issuance when the Shares are issued.

Based on the foregoing, we are of the opinion that, when and to the extent issued in exchange for the OP Units as provided in the Partnership Agreement, the Shares will be validly issued, fully paid and non-assessable.

Boston Properties, Inc.

April 1, 2011

Page 2

This opinion is being furnished to you for submission to the Commission as an exhibit to the Company’s Current Report on Form 8-K relating to the Shares (the “Current Report”), which is incorporated by reference in the Registration Statement. We hereby consent to the filing of this opinion as an exhibit to the Current Report and the said incorporation by reference and to the use of the name of our firm therein. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.