The synthesis ofcis- and trans-1,6-dihydroxypyrrolizidine starting fromtrans-4-hydroxyl-L-proline and their evaluation as glycosidase inhibitors are reported. Thecis-isomer was found to be a potent inhibitor against alpha-glucosidase and showed weak inhibitory effect against other glycosidases. Thetrans-isomer exhibited weak inhibitions of b-glucosidase and amyloglucosidase and poor inhibition of other glycosidases.