Abstract: The study results show that the optimum coagulating temperature of kid rennet is 45℃. The coagulating activity of kid rennet has some loss with heating treatment over 35℃, and at 60℃ after 10 minutes of heating treatment, the kid rennet activity loses completely. The coagulating activity increases with the decrease of milk pH between 5 and 8.Treating kid rennet for 20 hours at the pH between 2.5 and 7.5, the coagulating activity maintains stable. The Ca²⁺ has an obvious function to accelerate milk coagulation. The influence of substrate concentration on enzymatic activity is consistent with the Michaelis law.