Research has been done on the physicochemical characterization of purified alkaline proteases were isolated from A. thermoaerophilus SR-09. Measurement activities of alkaline protease are determined by the method of Walker, enzyme protein content was determined by Lowry method. Results showed that the optimum enzyme alkaline protease is at a temperature of 70°C with a pH of 8.5. The enzyme is stable to heat and alkaline conditions, alkaline protease enzyme belonged to the serine protease and where casein as a substrate specific; the enzyme is stable against surfactants and oxidants.