Abstract: Mucor racemosus 137 was isolated from fermented bean curd and brought to mutation by radiation of CO2 laser. The duration for radiation was 40s with distance of 22cm, and the diameter of laser beam was 0.4cm. High proteinase-producing mutant MR137-3 was obtained after screening cultures. The MR137-3 was found to have stable proteinase-producing activity in descendant cultures. The optimal culturing could be obtained at 30℃, pH6.0, culturing duration of 72h, with water content of 65% of culture medium.