Calf rennet has been used in Domiati cheese making for long times. Calf rennet is traditionally obtained from slaughtered calves. However, due to shortage of meat, calves were recommended to be fattened for two years. This cause a sharp decrease of calf rennet available. Researches have been trying to evaluate the applicability of calf rennet substitutes. These substitutes are : adult bovine rennet (ABR), microbial rennet from Mucor miehei (MR) and mixtures of calf rennet and adult bovine rennet at different ratio . This study was intended to evaluate different close of rennet as alternative to Calf rennet in coagulant milk and factors affecting the enzymes activity.                 Results showed that milk clotting time was positive correlated with sodium chloride concentration. But milk clotting time was inversely correlated with calcium chloride concentration and temperature. Milk clotting time was decreased as milk solids increased up to 12% under all treatments.