Aspergillus awamori possesses the ability to digest raw starches. For the effective utilization of starchy crops in South-Asian countries, it is important to digest raw starches without cooking for the industrial fermentation process. In this study, mutant strains of Aspergillus awamori IFO4033 with increased activity of α-amylase were isolated from freeze dried spores irradiated with C⁵⁺ ion-beams. The frequency of the mutation and the activity were higher for C⁵⁺-irradiated samples than those for gamma-irradiated ones. Compared to the digestibility of raw starches from cassava, sago and sukun by the parent strain, it increased two- to threefold by some mutant strains obtained from C⁵⁺ ion-beam irradiated spores.