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                                                                     Exhibit 5.1




                               February 1, 1999



Cabot Industrial Trust
Cabot Industrial Properties, L.P.
Two Center Plaza, #200
Boston, MA 02108-1906

          Re:  Registration Statement on Form S-3

Ladies and Gentlemen:

     We have acted as counsel to Cabot Industrial Trust, a Maryland real estate
investment trust (the "Company"), in connection with the proposed sale of
certain securities of the Company, as set forth in the Form S-3 Registration
Statement (the "Registration Statement") filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended (the "Securities Act"),
to which this opinion is an exhibit and the prospectus (the "Prospectus") which
is a part of the Registration Statement.  The Prospectus states that it will be
supplemented in the future by one or more supplements to the Prospectus (each, a
"Prospectus Supplement").  The Prospectus as supplemented by the various
Prospectus Supplements will provide for the sale of: (i) common shares of
beneficial interest, par value $.01 per share ("Common Shares"), (ii) preferred
shares of beneficial interest, par value $.01 per share ("Preferred Shares"),
(iii) Preferred Shares represented by depositary shares ("Depositary Shares"),
(iv) warrants to purchase Common Shares or Preferred Shares ("Warrants"), and
(v) guarantees of Debt Securities (as defined below) ("Guarantees").

     We have also acted as counsel to Cabot Industrial Properties, L.P., a
Delaware limited partnership of which the Company is the sole general partner
(the "Operating Partnership"), in connection with the proposed sale of its
senior debt securities ("Debt Securities" and, together with the Common Shares,
Preferred Shares, Depositary Shares, Warrants and Guarantees, the "Securities"),
as set forth in the Registration Statement and the Prospectus.  The Debt
Securities will be issued pursuant to an indenture among the Operating
Partnership, the Company and a corporate trustee, as trustee (the "Trustee"), 
(the "Indenture"), a form of which Indenture has been provided to us.

 
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Cabot Industrial Trust
February 1, 1999
Page 2


     As counsel to the Company and the Operating Partnership, we are generally
familiar with the proceedings taken and proposed to be taken by the Operating
Partnership and the Company in connection with the authorization and issuance of
the Securities and, for the purposes of this opinion, have assumed such
proceedings will be timely and properly completed in the manner presently
proposed and that the terms of each issuance will otherwise be in compliance
with law.

     As counsel to the Company, we have examined originals or copies certified
or otherwise identified to our satisfaction as being true and complete copies of
the Company's Declaration of Trust (the "Declaration of Trust"), the Company's
Amended and Restated Bylaws, resolutions of the Company's Board of Trustees and
such records, certificates and other documents, and have considered such
questions of law as we have considered necessary or appropriate for the purpose
of this opinion. As to certain matters of fact relevant to our conclusions
expressed in this opinion, we have relied upon certificates of public officials
and written or oral statements or other representations of officers of the
Company. In rendering such opinion, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals and
the conformity to authentic original documents of all documents submitted to us
as copies.

     As counsel to the Operating Partnership, we have examined originals or
copies certified or otherwise identified to our satisfaction as being true and
complete copies of the Operating Partnership's Second Amended and Restated
Agreement of Limited Partnership and resolutions of the Company's Board of
Trustees of the Company as the general partner of the Operating Partnership and
such records, certificates and other documents, and have considered such
questions of law as we have considered necessary or appropriate for the purpose
of this opinion. As to certain matters of fact relevant to our conclusions
expressed in this opinion, we have relied upon certificates of public officials
and written or oral statements or other representations of officers of the
Company. In rendering such opinion, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals and
the conformity to authentic original documents of all documents submitted to us
as copies.

     This opinion is given on the assumption that the Registration Statement and
any required post-effective amendments thereto have all become effective under
the Securities Act and that all issuances of Securities have been authorized by
the Board of Trustees.

     Based upon and subject to the foregoing and to the assumptions, conditions
and limitations set forth herein, we are of the opinion that:

     (1) when (a) the Common Shares have been duly established in accordance
with the provisions of the Company's Declaration of Trust, and (b) the Common
Shares have been duly executed and countersigned, and issued and sold in the
form and in the manner contemplated in 


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Cabot Industrial Trust
February 1, 1999
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the Registration Statement, including the Prospectus and the related Prospectus
Supplement(s), and (c) assuming that the terms of the Common Shares as executed
and delivered conform to the provisions of the Declaration of Trust in its
current form, the Common Shares will be legally issued, fully paid and non-
assessable;

     (2) when (a) the Preferred Shares have been duly established in accordance
with the provisions of the Company's Declaration of Trust and Articles
Supplementary (which shall have been accepted for record by the Maryland State
Department of Assessments and Taxation) setting forth the preferences,
conversion or other rights, voting powers, restrictions, limitations as to
dividends, and qualifications or terms or conditions of redemption, and (b) the
Preferred Shares have been duly executed and countersigned, and issued and sold
in the form and in the manner contemplated in the Registration Statement,
including the Prospectus and the related Prospectus Supplement(s), and assuming
that (c) the terms of the Preferred Shares as executed and delivered do not
violate any law applicable to the Company or result in a default under or breach
of any agreement or instrument binding upon the Company, and (d) the Preferred
Shares as executed and delivered comply with all requirements and restrictions,
if any, applicable to the Company, whether imposed by any court or governmental
or regulatory body having jurisdiction over the Company, the Preferred Shares
will be legally issued, fully paid and non-assessable;

     (3) when (a) the applicable deposit agreement (the "Deposit Agreement") has
been duly authorized, executed and delivered, and (b) the terms of a particular
issuance of Depositary Shares have been duly established in accordance with the
Deposit Agreement and applicable law, and (c) the depositary receipts (the
"Depositary Receipts") evidencing Depositary Shares, in the form contemplated
and authorized by the Deposit Agreement, have been issued by a depositary (the
"Depositary") and duly executed on behalf of the Depositary and delivered to and
paid for by the purchasers thereof in the manner contemplated by the
Registration Statement, including the Prospectus, the related Prospectus
Supplement(s) and any registration statement required to be filed under the
Securities Act in respect of the issuance of the Depositary Shares by the
Depositary (the "Depositary Registration Statement"), and (d) the Depositary
Registration Statement and any required post-effective amendments thereto have
all become effective under the Securities Act, and assuming that (e) the terms
of the Depositary Shares as executed and delivered are as described in the
Registration Statement, including the Prospectus, the related Prospectus
Supplement(s) and the Depositary Registration Statement, and (f) all corporate
action necessary for the issuance of such Depositary Shares and the underlying
Preferred Stock has been taken, and (g) the issuance of the Depositary Shares
and the underlying Preferred Stock do not violate any law applicable to the
Company or result in a default under or breach of any agreement or instrument
binding upon the Company, and (h) the Depositary Shares and the underlying
Preferred Stock comply with all requirements and restrictions, if any,
applicable to the Company, whether imposed by any court or governmental or
regulatory body having 
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Cabot Industrial Trust
February 1, 1999
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jurisdiction over the Company, and (i) the Depositary Shares are then issued and
sold as contemplated in the Registration Statement, including the Prospectus,
the related Prospectus Supplement(s) and the Depositary Registration Statement,
the Depositary Shares will be validly issued and will entitle the holders
thereof to the rights specified in the Depositary Receipts and the Deposit
Agreement;

     (4) when (a) the applicable warrant agreement (the "Warrant Agreement")
between the Company and a financial institution identified therein as warrant
agent (each, a "Warrant Agent") has been duly authorized, executed and
delivered, and (b) the Warrants have been duly established in accordance with
the terms of the Warrant Agreement and applicable law, and (c) the Warrants have
been duly executed and countersigned in accordance with the Warrant Agreement
relating to such Warrants, and issued and sold in the form and in the manner
contemplated in the Registration Statement, including the Prospectus and the
related Prospectus Supplement(s), and assuming that (d) the terms of the
Warrants as executed and delivered do not violate any law applicable to the
Company or result in a default under or breach of any agreement or instrument
binding upon the Company, and (e) the Warrants as executed and delivered comply
with all requirements and restrictions, if any, applicable to the Company,
whether imposed by any court or governmental or regulatory body having
jurisdiction over the Company, the Warrants will constitute valid and legally
binding obligations of the Company, enforceable against the Company in
accordance with their terms;

     (5) when (a) the Guarantees and the related Debt Securities have been duly
established in accordance with the terms of the Indenture (including, without
limitation, the adoption by the Board of Trustees of the Company, acting in its
own capacity and as general partner of the Operating Partnership, resolutions
duly authorizing the issuance and delivery of (i) the Guarantees by the Company
and (ii) the related Debt Securities by the Operating Partnership), and (b) the
Guarantees have been duly executed and delivered on behalf of the Company and
the related Debt Securities have been duly authenticated by the Trustee and duly
executed and delivered on behalf of the Operating Partnership against payment
therefor in accordance with the terms and provisions of the Indenture and as
contemplated by the Registration Statement, including the Prospectus and the
related Prospectus Supplement(s), and assuming that (c) the terms of the
Guarantees as executed and delivered are as described in the Registration
Statement, including the Prospectus and the related Prospectus Supplement(s),
and (d) the Guarantees as executed and delivered do not violate any law
applicable to the Company or result in a default under or breach of any
agreement or instrument binding upon the Company, the Guarantees will constitute
valid and legally binding obligations of the Company, enforceable against the
Company in accordance with their terms; and
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Cabot Industrial Trust
February 1, 1999
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     (6) when (a) the Debt Securities have been duly established in accordance
with the terms of the Indenture (including, without limitation, the adoption by
the Board of Trustees of the Company, in its capacity as general partner of the
Operating Partnership, of a resolution duly authorizing the issuance and
delivery of the Debt Securities), and have been duly authenticated by the
Trustee and duly executed and delivered on behalf of the Operating Partnership
against payment therefor in accordance with the terms and provisions of the
Indenture and as contemplated by the Registration Statement, including the
Prospectus and the related Prospectus Supplement(s), and assuming that (b) the
terms of the Debt Securities as executed and delivered are as described in the
Registration Statement, including the Prospectus and the related Prospectus
Supplement(s), and (c) the Debt Securities as executed and delivered do not
violate any law applicable to the Operating Partnership or result in a default
under or breach of any agreement or instrument binding upon the Operating
Partnership, and (d) the Debt Securities as executed and delivered comply with
all requirements and restrictions, if any, applicable to the Operating
Partnership, whether imposed by any court or governmental or regulatory body
having jurisdiction over the Operating Partnership, the Debt Securities will
constitute valid and legally binding obligations of the Operating Partnership,
enforceable against the Operating Partnership in accordance with their terms.

     The opinions set forth in paragraphs 3, 4, 5 and 6 above are subject to the
following exceptions, limitations and qualifications: (i) the effect of
bankruptcy, insolvency, reorganization, moratorium or other similar laws now or
hereafter in effect relating to or affecting the rights and remedies of
creditors; (ii) the effect of general principles of equity, whether enforcement
is considered in a proceeding in equity or at law, and the discretion of the
court before which any proceeding therefor may be brought; (iii) the
unenforceability under certain circumstances under law or court decisions of
provisions providing for the indemnification of, or contribution to, a party
with respect to a liability where such indemnification or contribution is
contrary to public policy; (iv) we express no opinion concerning the
enforceability of any waiver of rights or defenses with respect to stay,
extension or usury laws; and (v) we express no opinion with respect to whether
acceleration of the Debt Securities may affect the collectability of any portion
of the stated principal amount thereof which might be determined to constitute
unearned interest thereon.
 
     Insofar as the foregoing opinion involves matters governed by Maryland law,
we have relied, with your approval, upon the opinion of the law firm of Ballard
Spahr Andrews & Ingersoll and our opinion is subject to the assumptions,
limitations and qualifications set forth therein.

     We consent to the filing of this opinion as an exhibit to the Registration
Statement and to all references to our firm in the Registration Statement.
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Cabot Industrial Trust
February 1, 1999
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                              Very truly yours,


                              MAYER, BROWN & PLATT