5a-Carba-α-L-fucopyranose and -α-DL-fucopyranosylamine were synthesized in conventional manner starting from 2,3,4-tri-O-acetyl-6-bromo-6-deoxy-5a-carba-β-D- and -DL-glucopyranosyl bromides, respectively, and assayed for inhibitory activity against α-fucosidase (bovine kidney). Although the former proved to be only a moderate inhibitor (K(i) = 4.3 x 10-5 M), the latter could be shown to possess strong inhibitory potential (K(i) = 2.3 x 10-7 M). Diastereoisomeric imino-linked 5a'-carbadisaccharides were synthesized by coupling of the racemic 5a-carba-α-fucopyranosylamine and 1,6:3,4-dianhydro-2-azido-2-deoxy-β-D-galactopyranose, in order to estimate approximately the inhibitory activity of individual optical antipodes of 5a-carba-α-fucopyranosylamine.