Kidney bean seeds contain a proteinous inhibitor against α-amylase activities. The effect of the α-amylase inhibitor on larval growth and α-amylase activities was examined in three weevil species, Callosobruchus chinensis, C. maculatus and Zabrotes subfasciatus. The α-amylase inhibitor was mixed with azuki bean meal for a 0.5% concentration. Larvae of C. chinensis and C. maculatus, species unable to grow on kidney bean seeds, could not develop by feeding on the artificial beans and died before the second inster. The inhibitor markedly suppressed the α-amylase activity in the larval midgut of the two weevil species. On the other hand, larvae of Z. subfasciatus, a well known pest of kidney bean seeds, fed and developed on the artificial beans, and the larval midgut amylase activity of the weevil was not appreciably affected. The results suggest that the resistance of kidney beans to the three weevils is closely related to the inhibition of the larval amylase activity by the α-amylase inhibitor.