A novel 1-deoxynojirimycin derivative, (6S)-6-C-ethyl-1-deoxynojirimycin, was synthesized and tested on a set of α- and β-glucosidases. Its enzyme inhibitory activity against α-glucosidases from yeast and rice was superior to those of 1,5,6-trideoxy-6-fluoro-1,5-imino-D-glucitol, 1-deoxynojirimycin and its bicyclic analogue, castanospermine.