Several polyhydroxylated alkaloids were isolated from the extracts of freeze-dried silkworm powder, and purified by ion exchange chromatographic analysis. Through the HPLC analysis, we could identify 1-deoxynojirimycin (DNJ) and a kind of calystegin $B_2$ (HS-58) as well as a noble compound (HS-74) from the purified polyhydroxylated alkaloids. In order to know the characteristics of these isolated alkaloids as enzyme inhibitors, glycosidase inhibition activities of these identified alkaloids including other two non-purified alkaloids (SWP 3-1 and SWP 3-2) were investigated.