Chymosin, commonly known as rennin, is the main milk-coagulating enzyme available in rennet. RNA was extracted from the abomasum of a suckling calf water buffalo and was subjected to RT-PCR using degenerate primers to amplify 850bp of the chymosin gene. The sequence was aligned with 19 different mammals' chymosin genes. The sequence revealed that there is a similarity to them ranging from 64% to 98%. The purified recombinant proteins were obtained from the transformed E. coli and yeast. The clotting activity of both of the resulting proteins was examined compared to the commercial peers. It was noticed that the concentration of the purified protein ranged from 15,000 to 40,000 MCU. Therefore, the activity of the obtained proteins was the same and it was 105% when compared to the commercial peer. Having examined the cytotoxicity of the purified proteins, the results revealed no toxicity. We can conclude that the obtained recombinant protein is more active and safe even when expressed in bacteria rather than yeast.