The regulation of enzyme activity in the production of various fermented foods using koji mold has been optimized in many ways, and few additional refinements are apparent. This study examined light as a modifiable factor with which to adjust the enzyme activities of koji. A previous study has shown improved saccharification of wheat bran with Aspergillus oryzae RIB40 under at least 8 h of darkness. In the work reported here, light exposure had no significant effect on the saccharification activity of A. oryzae RIB1187. However, light exposure for 8 h or more continuously decreased protease-specific activity in RIB1187, as was seen previously in RIB40. This information may help manufacturers to improve fungal enzyme production, processes, and facilities.