Two types of alkaline serine proteases were isolated from the culture filtrate of an alkalophilic actinomycete, Nocardiopsis dassonvillei OPC-210. The enzymes (protease I and protease II) were purified by acetone precipitation, DEAE-Sephadex A-50, CM-Sepharose CL-6B, Sephadex G-75 and phenyl-Toyopearl 650 M column chromatography. The purified enzymes showed a single band on sodium dodecyl sulphate polyacrylamide gel electrophoresis. The molecular weights of proteases I and II were 21,000 and 36,000, respectively. The pIs were 6.4 (protease I) and 3.8 (protease II). The optimum pH levels for the activity of two proteases were pH 10-12 (protease I) and pH 10.5 (protease II). The optimum temperture for the activity of protease I was 70 degrees C and that for protease II was 60 degrees C. Protease I was stable in the range of pH 4.0-8.0 up to 60 degrees C and protease II was stable in the range of pH 6.0-12.0 up to 50 degrees C.