Exhibit 8.1



                    [Letterhead of Sullivan & Cromwell LLP]








                                                    March 24, 2006




UBS AG,
      Bahnhofstrasse 45,
           Zurich,
                Switzerland.



UBS Preferred Funding Trust V,
      c/o Wilmington Trust Company,
           1100 North Market Street,
                Wilmington, Delaware 19890.



UBS Preferred Funding Trust VI,
      c/o Wilmington Trust Company,
           1100 North Market Street,
                Wilmington, Delaware 19890.



UBS Preferred Funding Trust VII,
      c/o Wilmington Trust Company,
           1100 North Market Street,
                Wilmington, Delaware 19890.



UBS Preferred Funding Trust VIII,
      c/o Wilmington Trust Company,
           1100 North Market Street,
                Wilmington, Delaware 19890.


UBS Preferred Funding Trust IX,
      c/o Wilmington Trust Company,
           1100 North Market Street,
                Wilmington, Delaware 19890.



Ladies and Gentlemen:

      As counsel to UBS AG (the "Company"), UBS Preferred Funding Trust V, UBS
Preferred Funding Trust VI, UBS Preferred Funding Trust VII, UBS Preferred
Funding Trust VIII and UBS Preferred Funding Trust IX (together with UBS
Preferred Funding Trust V, UBS Preferred Funding Trust VI, UBS Preferred Funding
Trust VII and UBS Preferred Funding Trust VIII, the "UBS Preferred Funding
Trusts") in connection with the registration of an unspecified aggregate initial

UBS AG                                                                      -2-

offering price or number of the debt securities and warrants to be issued (on a
delayed and continuous basis) by the Company and an unspecified aggregate
initial offering price or number of the trust preferred securities to be issued
(on a delayed and continuous basis) by the UBS Preferred Funding Trusts, in each
case, pursuant to each base prospectus (each a "Prospectus") that forms a part
of the registration statement on Form F-3 of the Company and the UBS Preferred
Funding Trusts filed with the Securities and Exchange Commission on March 27,
2006 (the "Registration Statement") to which this opinion is filed as an
exhibit, we hereby confirm to you that the discussions set forth under the
heading "U.S. Tax Considerations" contained in each Prospectus in the
Registration Statement is our opinion, subject to the limitations set forth
therein.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to each reference to us under the heading "U.S. Tax
Considerations" in each Prospectus in the Registration Statement. 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 Securities Act of 1933.

                                                     Very truly yours,



                                                     /s/ SULLIVAN & CROMWELL LLP