Bacillus subtilis mutant with improved protease activity was obtained using DES treatment.The approximate molecular weight of this protease was obtained using gelatin as a substrate,and effects of mercaptoethanol on the protease activity were detected as well.The protease was treated under different temperatures and pH conditions.The enzyme activity was examined using ninhydrin.The molecular weight of the purified enzyme was estimated to be 100 ku by SDS-PAGE.The optimum pH and temperature was 6.0,50 ℃.About 50% enzymatic activity was retained after incubation at 70 ℃ for 10 min.The enzyme activity was significantly influenced by mercaptoethanol.Based on the difference of molecular weight and optimum pH from reported protease of Bacillus subtilis,it indicated that this protease was a new-type with wide applications.