Exhibit 5.1
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               [On Cleary, Gottlieb, Steen & Hamilton Letterhead]




                                                     October 29, 2003


Morgan Stanley & Co. Incorporated
1585 Broadway
New York, New York 10036

MS Structured Asset Corp.
1585 Broadway
New York, New York 10036

Ladies and Gentlemen:

         We have acted as special counsel to MS Structured Asset Corp. (the
"Depositor") in connection with the formation of Structured Asset Trust Unit
Repackagings ("SATURNS") Trust No. 2003-15 (the "Trust"), the issuance by the
Trust of $25,000,000 principal amount of Class A Units (the "Class A Units") and
$25,000,000 notional amount of Class B Units (the "Class B Units" and together
with the Class A Units, the "Units"), and the offer and sale of the Units by the
Underwriter. The Units are offered pursuant to a registration statement on Form
S-3 (No. 333-101155). Such registration statement, as amended when it became
effective, but excluding the documents incorporated by reference therein, is
herein called the "Registration Statement," and the related prospectus, as
supplemented by the prospectus supplement dated October 24, 2003 and the
prospectus supplement dated October 29, 2003 relating to the Class A Units, and
by the prospectus supplement relating to the Class B Units dated October 29,
2003 and as first filed with the Securities and Exchange Commission pursuant to
Rule 424(b)(2) under the Securities Act, but excluding the documents
incorporated by reference therein, is herein called the "Prospectus." This
opinion letter is furnished pursuant to Section 4(c) of the Underwriting
Agreement dated October 29, 2003 (the "Underwriting Agreement") between the
Depositor and the Underwriter. The Trust is organized under the laws of the
State of New York, pursuant to the Trust Agreement, dated October 29, 2003 (the
"Trust Agreement"), between LaSalle Bank National Association, as trustee (the
"Trustee") and the Depositor, which Trust Agreement, to the extent provided
therein, incorporates by reference the Standard Terms referenced therein. Unless
otherwise defined herein, capitalized terms used herein shall have the meanings
ascribed thereto in the Trust Agreement.

         In arriving at the opinions expressed below, we have reviewed the
following documents:

         (a) the Prospectus and the documents incorporated by reference therein;

         (b) the Trust Agreement; and

         (c) the Class A Units.

         In addition, we have reviewed the originals or copies certified or
otherwise identified to our satisfaction of all such corporate records of the
Depositor and such other instruments and other certificates of public officials,
officers and representatives of the Depositor and such other persons, and we
have made such investigations of law, as we have deemed appropriate as a basis
for the opinions expressed below.

         In rendering the opinions expressed below, we have assumed the
authenticity of all documents submitted to us as originals and the conformity to
the originals of all documents submitted to us as copies. In addition, we have
assumed and have not verified the accuracy as to factual matters of each
document we have reviewed (including, without limitation, the accuracy of the
representations and warranties of the Depositor in the Standard Terms).

         Based on the foregoing, and subject to the further assumptions and
qualifications set forth below, it is our opinion that:

         1. Assuming the Trust Agreement has been duly authorized, executed and
delivered by each of the Trustee and the Depositor, the Trust Agreement is the
valid and binding obligation of the Depositor enforceable against the Depositor
in accordance with its terms.

         2. The Class A Units, assuming that they have been duly and validly
authorized, executed, and issued by the Trustee, authenticated as specified in
the Trust Agreement and delivered to the Depositor, have been legally and
validly issued, the holders of the Class A Units will be entitled to the
benefits of the Trust Agreement, and the Class A Units are fully paid and
nonassessable.

         Insofar as the foregoing opinions relate to the validity, binding
effect or enforceability of any agreement or obligation (a) we have assumed that
each other party to such agreement or obligation other than the Depositor has
satisfied those legal requirements that are applicable to it to the extent
necessary to make such agreement or obligation enforceable against it, and (b)
such opinions are subject to applicable bankruptcy, insolvency and similar laws
affecting creditors' rights generally and to general principles of equity.

         The foregoing opinions are limited to the federal law of the United
States of America, and the law of the State of New York.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and the reference to this firm in the Registration
Statement and the related Prospectus under the caption "Validity of Units". By
giving such consent, we do not admit that we are "experts" within the meaning of
the Act, or the rules and regulations of the Commission issued thereunder with
respect to any part of the Registration Statement, including this exhibit.

                                          Very truly yours,

                                          CLEARY, GOTTLIEB, STEEN & HAMILTON



                                          By  /s/ Michael A. Mazzuchi
                                              --------------------------------
                                              Michael A. Mazzuchi, a Partner