In order to detect the proteases in the 1 mol/L NaCl extract of plant PSⅡ particles and its 1 mol/L NaCl extract, gelatin-SDS-polyacrylamide gel electrophoresis was used. Six proteases with molecular mass of 34,37,50,54,58 and 68 ku were detected. Influence of reducer and ion strength on the activity of proteases was analyzed preliminary. The new approach is convenient and highly sensitive for separation and detection of proteases at the same time.