This study described the screening of alpha-amylase and alpha-glucosidase inhibitory activity in hot water and ethanol extracts of 195 species of wild/cultivated mushrooms. Tricholoma giganteum (Nioushimeji), Russula nigricans (Kurohatsu), Morchella esculenta (Amigasatake) and so on showed potent alpha-amylase inhibitory activity, and Boletus pseudocalopus (Niseashibeniiguchi), Cortinarius alboviolaceus (Usufujifuusentake), Cortinarius armillatus (Tsubafuusentake), Dictyophora indusiata (Kinugasatake) and so on showed potent alpha-glucosidase inhibitory activity. When they are compared using IC50 data, alpha-glucosidase inhibition activity of these mushrooms was stronger than alpha-amylase inhibition activity of them. Active components of alpha-glucosidase inhibition activity were indentified as nojirimycin derivatives; alpha-homonojirimycin and o-beta-D-glucopyranosyl-alpha-homonojirimycin, in four mushrooms such as B. pseudocalopus, C. armillatus, C. alboviolaceus, and D. indusiata using LC-TOFMS. Total nojirimycin derivative contents seemed to be correlated with alpha-glucosidase inhibitory activity. Therefore, it was suggested that the main active components of alpha-glucosidase inhibitory activity were nojirimycin derivatives regarding these four mushrooms. (Received Jul. 5, 2010; Accepted Aug. 30, 2010)