Objective The kinds and activities of proteolytic enzymes of organs in the digestive system of Grus grus were studied to provide basic information for the taxonomy and evolvement study of wild birds. Methods The experiment was carried out at 4℃ by using gelatine polyacrylamide gel electrophoresis(GPAGE) ameliorat. Results 1 Altogether 26 kinds of proteolytic enzymes were found in the digestive system of Grus grus in all pH value conditions. 2 The kinds and activities of proteolytic enzymes in the digestive system of Grus grus were affected by pH. The activities of proteolytic enzymes were weakest in the acid environment and strongest in the neutral environment, which shows that the activities of the neutral proteolytic enzymes were stronger than those of the alkaline proteolytic enzymes, and those of the acid proteolytic enzymes were weakest.3. The kinds and activities of proteolytic enzymes of the same organ varied tremendously in different pH value conditions. The proteolytic enzymes of different organs had different optimal pH values. 4. Proteolytic enzymes with 19?kD molecular weight existed in every organ of the digestive system except glandular stomach in all pH conditions. Proteolytic enzyme with 66 and 22?kD molecular weight was found in every organ of the digestive system in the neutral environment. Conclusion The optimal pH value of proteolytic enzymes in the digestive system of Grus grus is 7.0. The distr