Using casein as a substrate, the kinetic characteristics of protease from Acer truncatum Bunge leaf was studied. Michaelis-Menten constant(Km) and the maximal reaction rate(Vmax) of the protease were determined under different temperatures(40℃-80℃) and different pH values(pH 6.5-pH 8.5).The results indicated that the Km decreased and the Vmax increased when temperature increased from 40℃ to 80℃.The Km decreased and Vmax increased with pH values rising from pH 6.5 to pH 7.5,but the Km increased and Vmax decreased with pH values rising from pH 7.5 to pH 8.5.The results show that the proper pH of enzymatic reaction of the protease is pH 7.5.