The polypeptides were prepared from silver carp skin by the method of mixed enzymatic hydrolysis,and divided into SP1(＞6 ku),SP2(3-6 ku) and SP3(＜3 ku) by ultrafiltration. The antioxidant capacity in vitro of three polypeptides and the amino acid composition of SP1 and SP3 were analyzed. It was suggested that SP3 has the strongest antioxidant capacity in vitro. Subsequently,the antioxidant capacity in vivo of SP3 was measured. The results showed that the order of hydroxyl radical scavenging rate,superoxide anion radical scavenging rate and reducing ability in the three polypeptides was SP3＞SP2＞SP1,but there was no significant difference in chelating rate of copper ions. Analysis of amino acid composition showed that the percentage of hydrophobic amino acid in SP3 was significantly higher than SP1. Besides, compared with the injured group,SP3 group had higher indexes of liver and spleen. Furthermore,SP3 significantly increased the activities of SOD,GSH-Px and CAT and decreased the content of MDA in serum and liver. In conclusion,SP3 has better antioxidant activity than SP1 and SP2.