<DOCUMENT>
<TYPE>EX-5.1
<SEQUENCE>3
<FILENAME>ex5-1.txt
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           [LETTERHEAD OF WILMER CUTLER PICKERING HALE AND DORR LLP]


                                                                     Exhibit 5.1


September 1, 2004

Franklin Street Properties Corp.
401 Edgewater Place, Suite 200
Wakefield, MA 01880


      Re:   Registration Statement on Form S-4

Ladies and Gentlemen:

      This opinion is furnished to you in connection with a Registration
Statement on Form S-4 (the "Registration Statement") filed with the Securities
and Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended (the "Securities Act"), for the registration of an aggregate of
10,894,994 shares of Common Stock, $0.0001 par value per share (the "Shares"),
of Franklin Street Properties Corp., a Maryland corporation (the "Company"),
issuable pursuant to the Agreement and Plan of Merger, dated August 13, 2004, by
and among the Company, Montague Acquisition Corp., Addison Circle Acquisition
Corp., Royal Ridge Acquisition Corp. and Collins Crossing Acquisition Corp.,
each a Delaware corporation and wholly-owned subsidiary of the Company, and FSP
Montague Business Center Corp., FSP Addison Circle Corp., FSP Royal Ridge Corp.
and FSP Collins Crossing Corp., each a Delaware corporation (the "Merger
Agreement").

      We are acting as counsel for the Company in connection with the issuance
by the Company of the Shares. We have examined signed copies of the Registration
Statement as filed with the Commission. We have also examined and relied upon
the Merger Agreement, minutes of meetings of the Board of Directors of the
Company as provided to us by the Company, stock record books of the Company as
provided to us by the Company, the Articles of Organization and By-Laws of the
Company, each as amended to date, and such other documents as we have deemed
necessary for purposes of rendering the opinions hereinafter set forth.

      In our examination of the foregoing documents, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to original documents of all documents submitted to
us as copies, the authenticity of the originals of such latter documents and the
legal competence of all signatories to such documents.

      We assume that the appropriate action will be taken, prior to the issuance
of the Shares in accordance with the Merger Agreement, to register and qualify
the Shares for sale under all applicable state securities or "blue sky" laws.

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Franklin Street Properties Corp.
September 1, 2004
Page 2


      We express no opinion herein as to the laws of any state or jurisdiction
other than the state laws of the State of Maryland, the General Corporation Law
of the State of Delaware and the federal laws of the United States of America.

      Based upon and subject to the foregoing, we are of the opinion that the
Shares to be issued by the Company have been duly authorized for issuance and,
when the Shares are issued in accordance with the terms and conditions of the
Merger Agreement, the Shares will be validly issued, fully paid and
nonassessable.

      It is understood that this opinion is to be used only in connection with
the issuance of the Shares while the Registration Statement is in effect.

      Please note that we are opining only as to the matters expressly set forth
herein, and no opinion should be inferred as to any other matters. This opinion
is based upon currently existing statutes, rules, regulations and judicial
decisions, and we disclaim any obligation to advise you of any change in any of
these sources of law or subsequent legal or factual developments which might
affect any matters or opinions set forth herein.

      We hereby consent to the filing of this opinion with the Commission as an
exhibit to the Registration Statement in accordance with the requirements of
Item 601(b)(5) of Regulation S-K under the Securities Act and to the use of our
name therein and in the related Prospectus under the caption "Legal Matters." In
giving such consent, we do not hereby 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 of the Commission.



Very truly yours,

WILMER CUTLER PICKERING HALE AND DORR LLP



By:   /s/ Jeffrey A. Hermanson
      -------------------------------
      Jeffrey A. Hermanson, a Partner


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