Abstract: The protease produced by the fermentation of strain HS18, which isolated from the intestinal of Pinctada martensi and identified as Bacillus subtilis.A protease with high purity from the fermentation of Bacillus subtilis HS18 was purified by precipitation with ammonium sulfate, DEAE-Sephadex A-50column chromatography and Sephadex G-100 gel filtration chromatography and its recovery rate was 11.4%.The protease was determined by SDS-PAGE to have a molecular weight of 31ku.The optimal pH and temperature of the protease were 10.0 and 50℃, respectively.In addition, this protease could be activated by divalent cations such as K+ and Na+ and inhibited by serine-protease inhibitors (PMSF) .All results showed that this alkaline protease was a serine-protease.