Abstract Several glycosides of calystegines B 1 and B 2 were synthesized by use of rice α-glucosidase and the whole cells of Rhodotorula lactosa, and their glycosidase inhibitory activities were investigated. Incubation of a mixture of calystegine B 1 and maltose with rice α-glucosidase gave 3-O-α- d-glucopyranosylcalystegine B 1 ( 2, 11.3%). An enzymatic β-transglucosylation reaction of calystegines B 1 or B 2 with cellobiose using the whole cells of R. lactosa gave 3-O-β- d-glucopyranosylcalystegine B 1 ( 1) (0.9%) or 4-O-β- d-glucopyranosylcalystegine B 2 ( 3, 11.2%), respectively, while a similar β-transgalactosylation of calystegine B 2 from lactose gave 4-O-β- d-galactopyranosylcalystegine B 2 ( 4, 10.1%). The glycosylation of calystegines B 1 and B 2 markedly decreased or abolished their inhibition against β-glucosidase, α- or β-galactosidase. Compound 4 however retained more or less the potency of calystegine B 2 against trehalase. Interestingly, compound 1 was a noncompetitive inhibitor of rice α-glucosidase, with a K i value of 0.9 ± 0.1 μM.