Abstract: Four lactobacillus helveticus with high proteolytic activity were regarded as the research subject, the changes in degree of hydrolysis (DH) and pH were examined periodically during 36 hours of fermentation.One of strains was selected for further study.Fermentation condition was optimized by response surface analysis and the hydrolyzates were determined by SDS- PAGE.The results showed that optimum hydrolysis condition was as follows:inoculum size of 3.5%, substrate concentration of 13%, hydrolysis temperature of 37.0℃, fermentation time of 18h.The degree of hydrolysis was 5.60% and the hydrolyzates contained a large number of small peptide fragments.So the strain was an optimal strain for the production of small peptides derived from fermented milk.