Abstract: In order to control the quality of cheese, the hydrolysis of protein(measured by SDS-gel electrophoresis and soluble nitrogen), the changes of texture in non-melting cheese and the changes of functional properties in melting cheese were studied during ripening of Mozzarella cheese. Due to rennet and lactobacillus enzymes contributed to the proteolysis, both the pH4.6 acetate buffer soluble nitrogen and 12% TCA-soluble nitrogen increased during cheese ripening. The rennet influences only the extent of casein degradation; however, lactobacillus and lactobacillus enzymes influence not only the extent but also the depth of casein degradation. Casien is first degraded into high molecular mass peptides by residual rennet and lactobacillus enzymes, then the high molecular mass peptides are furtherly degraded into low molecular mass peptides and free amino acids by lactobacillus enzymes. With the hydrolysis of casein, the TPA hardness and TPA springess of cheese decreased, while the meltability and free oil formatiom of cheese increased. The browning of cheese increases with the increase of the low molecular mass peptides and free amino acids.