In order to obtain new industrial koji molds with properties of both non-melanization and high glucoamylase activity, Aspergillus oryzae strains were mutated by irradiation of ultraviolet light. In the mutant strains, only one mutant, H-1 strain, with a high glucoamylase activity and a low tyrosinase activity like its parent strain was isolated. On the other hand, another mutant, G-4 strain, had higher activities of both enzymes than those of the parent strain. The amounts of glucoamylase produced by both mutant strains were more abundant than those of the parent strains. The specific activities and molecular weights of the glucoamylases of both mutant strains were almost equal to those of the parent strains. A fermentation test showed that the sake brewed by the H-1 strain had an excellent flavor and its sake cake did not turn brown even one month after Koji making and brewing at full-scale. The H-1 strain seems to be a practical, high quality strain for brewing sake with a sweet aroma, as it provided a high level of saccharification activity without browning of the sake cake.