To investigate the hydrolysis of glucosyl esters by beta -glucosidase, p-hydroxybenzoyl beta -D-glucose (pHBG) was chemically synthesized. The hydrolytic activity of some beta -glucosidases for pHBG was compared to that for p-nitrophenyl beta -glucoside (pNPG). The Clavibacter michiganense and Flavobacterium johnsonae enzymes could hydrolyze pHBG and steviol glycosides which are natural glucosyl esters. The commercial beta -glucosidase originating from Caldocellum saccharolyticum also hydrolyzes pHBG despite having no activity for steviol glycosides. The beta -glucosidase from Aspergillus niger cleaved the glucosyl ester linkage much more weakly than the glucosidic linkage. The pa-activity profile for the hydrolysis of pHBC was similar to that of pNPG by the C. saccharolyticum beta -glucosidase. The similar profiles for these substrates suggested that the active site for the glucosyl ester chemically resembles that for glucoside with respect to catalysis. Kinetic analysis of the C. saccharolyticum beta -glucosidase for mixed substrates of pHBG and pNPG showed that the hydrolysis of pHBG competed with that of pNPG. This result indicated that there is only one active site for both the glucosyl ester and glucoside. Mass spectroscopic analysis of the hydrolysates of pHBG in (H2O)-O-18 suggested that beta -glucosidase hydrolyzes glucosyl esters between the anomeric carbon of glucose and the carbonyl oxygen, not between the carbonyl carbon and the carbonyl oxygen.