February 6, 1998


UST Corp.
40 Court Street
Boston, Massachusetts  02108

     Re:  UST CORP. REGISTRATION STATEMENT ON FORM S-4
          RELATING TO 3,300,000 SHARES OF COMMON STOCK

Ladies and Gentlemen:

     This opinion is rendered to you in connection with the filing by UST 
Corp., a Massachusetts corporation (the "Corporation") of its Registration 
Statement on Form S-4 (the "Registration Statement") with the Securities and 
Exchange Commission, relating to the registration under the Securities Act of 
1933 of 3,300,000 shares (the "Shares") of the Corporation's Common Stock, 
par value $0.625 per share (the "Common Stock"), filed with Securities and 
Exchange Commission on February 6, 1998, all of which Shares are to be 
issued to shareholders of Somerset Savings Bank ("Somerset"), in connection 
with the Corporation's acquisition of Somerset, pursuant to the terms of an 
Affiliation Agreement and Plan of Reorganization, dated as of December 9, 
1997 (the "Agreement"), among the Corporation and Somerset, and joined in by 
the Corporation's wholly-owned subsidiary, Mosaic Corp. on January 9, 1998.

     In rendering this opinion as General Counsel of the Corporation, I and 
an attorney in my office acting under my direction have participated with the 
Corporation and its officers in the preparation, review and filing of the 
Registration Statement and the related proxy statement-prospectus (the "Proxy 
Statement-Prospectus") included therein, have examined other corporate 
documents and records, have made such examination of law, and have discussed 
with the officers and directors of the Corporation and its subsidiaries such 
questions of fact as we have deemed necessary or appropriate.  We have also 
relied upon certificates and statements of such officers and directors as to 
factual matters and have assumed the genuineness of all signatures not known 
to us as well as the authenticity of all documents submitted to us as copies.



     Subject to the foregoing and to the proposed additional proceedings 
being taken as now contemplated prior to the issuance of the Shares, it is my 
opinion that the Common Stock has been duly authorized and, upon the issuance 
thereof in accordance with the Agreement, will be validly issued, fully paid 
and non-assessable.

     I hereby consent to the filing of this opinion as an Exhibit to the 
Registration Statement and to the use of my name in the Registration 
Statement and the related Proxy Statement-Prospectus.


                                       Very truly yours,

                                       /s/ Eric R. Fischer

                                       Eric R. Fischer,
                                       Executive Vice President,
                                       General Counsel and Clerk