Casein antimicrobial peptide of Mozzarella Cheese plays a very important role in human health.In order to study antibacterial activity of casein extract,the liquid was extracted from Mozzarella cheese after maturation for 40,50 and 60 days using sterile distilled water,acetic acid-sodium acetate buffer solution and TCA extraction.The antibacterial activity of cheese extract against Escherichia coli,Bacillus subtilis,S.cerevisiae and Aspergillus niger was investigated.The results showed that extracts from cheeses during different ripening stages all exhibited strong antimicrobial activity against Escherichia coli,Bacillus subtilis and S.cerevisiae.The extract obtained from cheese in mature stage of 40 days by sterile distilled water extraction showed strongest antimicrobial activity against Escherichia coli.The extract obtained from cheese in mature stage of 60 days by TCA extraction showed strongest antimicrobial activity against Bacillus subtilis,S.cerevisiae and Aspergillus niger.