The suicide substrate of isomalto-dextranase was designed, and the ω-epoxyalkyl α-glucosides, of which the alkyl carbons were three to six, were synthesized. The 2', 3'-epoxypropyl α-glucoside did not decrease the activity. ω-Epoxyalkyl α-glucosides with four to six alkyl carbons resulted in inactivation which followed the pseudo-first order kinetics. A detailed kinetic analysis on inactivation was done, and the results obtained supported that the compounds were suicide substrates for isomalto-dextranase. All ω-epoxyalkyl α-glucosides synthesized inactivated β-amylase. The C₅-al-kyl compound was the most effective for the inactivation of isomalto-dextranase, but β-amylase was strongly inactivated by the C₄-alkyl compound. The discrimination of inhibitors by the two en-zymes was considered to be based on the difference in their substrate recognition, in which β-amy-lase recognizes the maltosyl residue and isomalto-dextranase recognizes the isomaltosyl residue having one methylene group longer than the maltosyl residue. No inactivation for α-amylase was observed with the ω-epoxyalkyl α-glucosides. The 3', 4' epoxybutyl α-glucoside did not show any effect on the substrate binding. Conduritol B epoxide, a suicide substrate for α-glucosidase, also caused no inactivation or no inhibition of α-amylase activity. These findings were applied to the α-amylase assay in the enzyme mixture coexistent with β-amylase and α-glucosidase. Since 3', 4' ep-oxybutyl α-glucoside was hydrolyzed by α-glucosidase, a mixture of three enzymes was incubated with conduritol B epoxide at first, and then treated with 3', 4'-epoxybutyl α-glucoside, resulting in the complete inactivation of α-glucosidase and β-amylase. This procedure was shown to be useful in the determination of α-amylase in preparations containing α-glucosidase and β-amylase.