N-Substituted (3S,4S)- and (3R,4R)-pyrrolidine-3,4-diols 9 and 10, respectively, were derived from (+)-L- and (-)-D-tartaric acid, respectively. Compounds 9k, 91, and 9m with the N-substituents, BnNH(CH2)(2), 4-Phc(6)H(4)CH(2)NH(CH2)(2) and 4-ClC6H4CH2NH(CH2)(2), respectively, showed modest inhibitory activities toward aD-amyloglucosidases from Aspergillus niger and from Rhizopus mold (Table 1). Unexpectedly, several (3R,4R)-pyrrolidine-3,4-diols 10 showed inhibitory activities toward alpha-D-mannosidases from almonds and from jack bean (Table 3). N-Substitution by the NH2(CH2)(2) group, i.e., 10g, led to the highest potency.