<DOCUMENT>
<TYPE>EX-8.1
<SEQUENCE>4
<FILENAME>ex8-1.txt
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                                                                     Exhibit 8.1


                           [LETTERHEAD OF WILMERHALE]


                                  May 23, 2006

Franklin Street Properties Corp.
401 Edgewater Place
Suite 200
Wakefield, MA  01880-6210

      Re:   Certain Federal Income Tax Matters Related to Franklin Street
            Properties Corp.

Dear Ladies and Gentlemen:

      This opinion is being delivered to you in connection with certain federal
income tax matters related to Franklin Street Properties Corp. ("FSP Corp.") in
connection with the registration of shares of common stock of FSP Corp. as more
fully described in FSP Corp.'s Registration statement on Form S-3 filed with the
Securities and Exchange Commission on May 23, 2006 (the "Registration
Statement"). Except as otherwise provided, capitalized terms not defined herein
have the meanings set forth in the Registration Statement or in the letter
delivered to Wilmer Cutler Pickering Hale and Dorr LLP by FSP Corp. containing
certain representations of FSP Corp. relevant to this opinion (the
"Representation Letter"). All section references, unless otherwise indicated,
are to the United States Internal Revenue Code of 1986, as amended (the "Code").

      The conclusions expressed herein represent our judgment as to the proper
application of relevant provisions of the Code, Treasury Regulations, case law,
and rulings and other pronouncements of the Internal Revenue Service (the "IRS")
as in effect on the date of this opinion. No assurances can be given that such
laws will not be amended or otherwise changed, or that such changes will not
affect the conclusions expressed herein. Nevertheless, we undertake no
responsibility to advise you of any developments in the application or
interpretation of the income tax laws of the United States.

      Our opinion represents our best judgment of how a court would decide if
presented with the issues addressed herein and is not binding upon either the
IRS or any court. Thus, no assurances can be given that a position taken in
reliance on our opinion will not be challenged by the IRS or rejected by a
court.

      In our capacity as counsel to FSP Corp., and for purposes of rendering
this opinion, we have examined and relied upon the Registration Statement, the
Representation Letter, the Articles of Incorporation of FSP Corp. and the Bylaws
of FSP Corp., each as amended through the date hereof, and such other documents
as we considered relevant to our analysis. In our examination of documents, we
have assumed the authenticity of original documents, the accuracy of copies, the
genuineness of signatures, and the legal capacity of signatories.

      We have made such factual and legal inquiries, including examination of
the documents set forth above, as we have deemed necessary or appropriate for
purposes of our opinion. For purposes of rendering our opinion, however, we have
not made an independent investigation or audit of the facts set forth in any of
the above-referenced documents, including the Registration Statement and the
Representation Letter. We consequently have relied upon the representations
contained therein and assumed that the information presented in such documents
or otherwise furnished to us is accurate and complete in all respects relevant
to our opinion.

<PAGE>

Franklin Street Properties Corp.
May 23, 2006
Page 2


      In our review, we have assumed, with your consent, that all of the
obligations imposed by any documents on the parties thereto have been and will
be performed or satisfied substantially in accordance with their terms. We have
further assumed that during its taxable year ended December 31, 2002 and
subsequent taxable years that FSP Corp. and the Partnership Subsidiaries have
operated and will continue to operate in a manner that has made and will make
the representations and covenants contained in the Representation Letter true,
complete and correct for all such years. Moreover, we have assumed that FSP
Corp. and the Partnership Subsidiaries have been and will continue to be
operated in the manner described in the relevant partnership agreement, articles
(or certificate) of incorporation or other organizational documents and in the
Registration Statement. Finally, we have assumed that any statement in the
Representation Letter that is made "to the knowledge of", "belief of" or
similarly qualified is correct and accurate, and that such representation or
statement will continue to be correct and accurate, without such qualification.

      We also have assumed for the purposes of this opinion, without inquiry
with respect thereto, that FSP Corp. is a validly organized and duly
incorporated corporation under the laws of the State of Maryland. In the event
any of the statements, representations, or assumptions upon which we have relied
in rendering this opinion is incorrect or incomplete, our opinion could be
adversely affected and may not be relied upon.

Opinions

      Based upon the foregoing, and subject to the various assumptions,
limitations, and qualifications set forth in this letter, we are of the opinion
that:

      1. FSP Corp. was organized and has operated in conformity with the
requirements for qualification and taxation as a REIT under the Code for each
taxable year beginning with its taxable year ended December 31, 2002, and FSP
Corp.'s current organization and method of operation (as described in the
Registration Statement and the Representation Letter) will enable FSP Corp. to
continue to meet the requirements for qualification and taxation as a REIT.

      2. To the extent that the matters discussed under the heading "Material
United States Federal Income Tax Considerations" in the Registration Statement
constitute matters of law, they are accurate in all material respects.

      FSP Corp.'s qualification and taxation as a REIT depends upon FSP Corp.'s
ability to meet on a continuing basis, through actual annual operating and other
results, the various requirements under the Code and described in the
Registration Statement with regard to, among other things, the sources of its
gross income, the composition of its assets, the level of distributions to
stockholders, and the diversity of its share ownership. Wilmer Cutler Pickering
Hale and Dorr LLP will not review FSP Corp.'s compliance with these requirements
on an independent or ongoing basis. No assurance can be given that the actual
results of operations of FSP Corp., the sources of its income, the nature of its
assets, the level of FSP Corp.'s distributions to its shareholders and the
diversity of FSP Corp.'s share ownership for any given taxable year will satisfy
the requirements under the Code for qualification and taxation as a REIT or that
the relief provisions applicable to REITs will be available to FSP Corp.

      This opinion addresses only the specific United States federal income tax
consequences set forth above in the numbered paragraphs under the caption
"Opinions", and does not address any other federal, state, local, or foreign
income, estate, gift, transfer, sales, use, or other tax consequences that may
be applicable to FSP Corp.

      This opinion is intended for the purpose of inclusion as an exhibit to the
Registration Statement. It may not be relied upon for any other purpose and may
not be made available to any other person or entity without our prior written
consent. This opinion speaks only as of the date hereof, and we undertake no


<PAGE>

Franklin Street Properties Corp.
May 23, 2006
Page 3


obligation to update or supplement this opinion to reflect any changes of law or
fact (including without limitation our subsequent discovery of any facts that
are inconsistent with the Representation Letter). We hereby consent to the
filing of this opinion as an exhibit to the Registration Statement and further
consent to the use of our name in the Registration Statement in connection with
references to this opinion. In giving this consent, however, we do not hereby
admit that we are in the category of persons whose consent is required under
Section 7 of the Securities Act of 1933, as amended.

                                    Very truly yours,

                                    WILMER CUTLER PICKERING HALE AND DORR LLP

                                    By:  /s/ Kimberly B. Wethly
                                         --------------------------------------
                                         Kimberly B. Wethly, a Partner
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