Abstract: The study was conducted to discuss the effects of compound micro-ecological preparation peptin on the growth performance,diarrhea rate and microbial population of weaned piglets.45 Dingyuan black piglets were divided into three groups.The basal diet was added in control group and 0.1%,0.2% peptin were added to the basal diet in test groups.Each group had three repetitions and each repetitions included 5 piglets.The whole experiment lasted for 21 days.The results showed that the daily gain in test group 1 and test group 2 significantly increased 22.5% and 12.9% than control group respectively（P〈0.05）.And the feed-meat ratio in test group 1 and test group 2 significantly decreased 7.87%（P〈0.05）and 4.49%（P〉0.05）than control group respectively.On the 14th day,the number of Escherichia coli in test group 1 and test group 2 was 5.87% and 7.02% significantly lower than control group respectively（P〈0.05）.On the 21st day,the number of lactobacillus in test group 1 and test group 2 was 4.18% and 4.79% higher than control group respectively（P〈0.05）and the number of Escherichia coli in test group 1 and test group 2 was 6.68% and 7.84% lower than control group（P〈0.05）.IgG level in test group 1 and test group 2 significantly increased 18.5% and 22.4% than control group respectively（P〈0.05）.The content of total protein in test group 1 and test group 2 increased 9.46% and 7.21% than control group respectively（P〈0.05）.But serum urea nitrogen（SUN） in test group 1 and test group 2 decreased 22.9% and 25.1% than control group respectively（P〈0.05）.On the 14th day,SIgA level in test group 1 and test group 2 increased 27.8% and 30.6% than control group respectively（P〈0.05）.On the 21st day,SIgA level in test group 1 and test group 2 increased 33.0% and 30.1% than control group respectively（P〈0.05）.On the 14th day,the activities of protease in test group 1 and test group 2 increased 84.0%and 99.3% than control group respectively（P〈0.01）and amylase activities in test group 1 and test group 2 increased 3.98% and 7.65% than control group respectively（P〉0.05）.On the 21st day,the activities of protease in test group 1 and test group 2 increased 77.4% and 91.2% than control group respectively（P〈0.01）and amylase activities in test group 1 and test group 2 increased 13.1% and 14.3% than control group respectively（P〉0.05）.In conclusion,peptin could decrease the diarrhea rate of weaned piglets,enhance the growth performance,improve microbial population and enhance the immune function of weaned piglets.