The 12-tungstophosphoric acid (HPW) and its insoluble salts containing either caesium or ammonium cations were encapsulated into channels of a MCM-41 molecular sieve and they were used as catalyst for the liquid phase synthesis of Bisphenol-A From phenol and acetone. For comparison, zeolites ZSM-5, H-Y and dealuminated H-DY have also been tested in this reaction. The CsHPW/MCM system appeared to be the most selective towards p,p' isomer formation.