Protoplast fusion and recombinant DNA technologies have become important tools for the breeding of fungi. In order to apply protoplast fusion to the breeding of Monascus species (beni koji fungi), we attempted to isolate auxotrophic mutants of this fungi. We prepared rice koji using each of the 8 strains of the Monascus species, and measured amounts of N-acetylglucosamine, protease activity and two kinds of amylase activity in each koji sample. From this result, three strains, M. anka IFO4478, M. pilosus IFO4480 and M. purpureus AHU9451, were selected as the parent strain for protoplast fusion. The conidia from these strains were treated with UV and screened for mutants. Consequently, auxotrophic mutants were obtained in an efficiency of about 1 %; 7 mutants were obtained from M. anka, I from M. pilosus and 4 from M. purpureus. Five of the 7 mutants of. M. anka were adenine-requiring. The mutant of M. pilosus was biotin-requiring. Three of the mutants of M. purpureus required nicotinic acid, leucine or p-amino benzoic acid, respectively, for growth.