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                                                                     Exhibit 5.2

                       [SULLIVAN & CROMWELL LETTERHEAD]



                                                              September 28, 2000




UBS AG,
     Bahnhofstrasse 45,
        Zurich, Switzerland.

Dear Ladies and Gentlemen:

         In connection with the subordinated guarantee by UBS AG, a bank
organized under the laws of Switzerland, of the ___% Noncumulative Company
Preferred Securities to be issued by UBS Preferred Funding Company I, the terms
of which are established by the UBS AG Subordinated Guarantee Agreement (the
"Subordinated Guarantee Agreement"), we, as your counsel, have examined such
corporate records, certificates and other documents, and such questions of law,
as we have considered necessary or appropriate for the purposes of this opinion.

         Upon the basis of such examination, we advise you that, in our opinion,
assuming the due authorization, execution and delivery of the Subordinated
Guarantee Agreement, the Subordinated Guarantee Agreement will
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UBS AG                                                                       -2-


constitute a valid and legally binding obligation of UBS AG, subject to
bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and
similar laws of general applicability relating to or affecting creditors' rights
and to general equity principles.

         The foregoing opinion is limited to the Federal laws of the United
States and the laws of the State of New York and we are expressing no opinion as
to the effect of the laws of any other jurisdiction. With respect to the due
authorization, execution and delivery by UBS AG of the Subordinated Guarantee
Agreement, we have relied upon the opinion, dated September 29, 2000, of Bar &
Karrer, and our opinion is subject to the same assumptions, qualifications and
limitations with respect to such matters as are contained in such opinion of Bar
& Karrer.

         Also, we have relied as to certain matters on information obtained from
public officials, officers of UBS AG and other sources believed by us to be
responsible, and we have assume that the Subordinated Guarantee Agreement has
been duly authorized, executed and delivered by Wilmington Trust Company, an
assumption which we have not independently verified.
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UBS AG                                                                       -3-


         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to us under the heading "Validity of
the Securities" in the Prospectus. In giving such consent, we do not thereby
admit that we are in the category of persons whose consent is required under
Section 7 of the Act.


                                            Very truly yours,


                                            /S/ Sullivan & Cromwell