This experiment was conducted to investigate the effects of milk origin bioactive peptides on growth performance and serum biochemical parameters of tilapia ( Oreochromis aureus×O.niloticus). The study contained two experiments, experiment 1 was cell cultured  in vitro  experiment, and experiment 2 was feeding experiment. Experiment 1: In order to estimate the best enzyme source, three casein hydrolysate samples were prepared by different enzyme combinations (production 1: neutral protease and pawpaw protease combination, production 2: trypsin and neutral protease combination, production 3: trypsin), and used in liver cells cultured  in vitro experiment. Experiment 2: three hundred and sixty tilapia with an average body weight of (24.93±0.22) g were randomly allocated into 6 groups (groupⅠ was control group, group Ⅱ,Ⅲ,Ⅳ,Ⅴ and Ⅵ were test group) with 3 replicates in each group and each replicate contained 20 fish. Group Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ and Ⅵwere fed diet with 0, 0.1％, 0.2％, 0.4％, 0.8％ and 1.6％ milk origin bioactive peptides (hydrolysate of the best enzyme source), respectively. The experiment lasted for 8 weeks. The results showed that: (1) the effect of liver cells cultured  in vitro  of production 2 was significantly higher than that of control and production 1, 3 (P＜0.05); (2) the final weight, weigh gain ratio, specific growth ratio, feed conversion ratio, protein efficiency ratio of tilapia in group Ⅳ were significantly higher than that in control and the other test groups (P＜0.05); there were no significant differences in nutrient components of whole fish body and back muscle among six groups (P>0.05); the concentrations of compliment, lysozyme and high density lipoprotein in serum of tilapia test group were significantly higher than that in control group (P＜0.05), and that in group Ⅳ were significantly higher than that in group Ⅱ, Ⅲ, Ⅴand Ⅵ (P＜0.05); the concentrations of cholesterol in serum of tilapia in group Ⅵ was significantly higher than that in control group (P＜0.05), but no significant differences were found among the test groups. In conclusion, our study indicated that the most suitable dose of milk origin bioactive peptides in diet of tilapia was 0.4%.