An examination of the bulbs of Scilla socialis has resulted in the isolation of 11 hyacinthacines, two pyrrolidines, and three piperidines. The structures of the new alkaloids were elucidated by spectroscopic methods as beta-1-C-ethyldeoxymannojirimycin (5), hyacinthacines B7 (10), C2 (11), C3 (12), C4 (13), and C5 (14), and alpha-5-C-(3-hydroxybutyl)hyacinthacine A2 (15). Although, beta-l-homofuconojirimycin (3) and alpha-7-deoxyhomonojirimycin (alpha-7-deoxy-HNJ, 4) are previously known alkaloids, this is the first report of their occurrence in the plant family Hyacinthaceae. Alkaloid 11 was found to be a good inhibitor of bacterial beta-glucosidase and human placenta alpha-l-fucosidase, with IC50 values of 13 and 17 microM, respectively, while alkaloid 12 showed no inhibitory activity toward alpha-l-fucosidase but was a more potent inhibitor of bovine liver beta-galactosidase (IC50 = 52 microM) than 11. Alkaloids 13 and 14 were shown to be inhibitory toward mammalian alpha-glucosidase (IC50 = 45 and 77 microM, respectively), and alkaloid 14 was demonstrated as a moderate inhibitor of bacterial beta-glucosidase (IC50 = 48 microM).