As sea cucumber gonad， Apostichopus japonicus (Aj) sperm is rich in protein， polysaccharide and many kinds of active substances. It was collected separately and enzymatically hydrolyzed to develop new marine active peptides. In this paper， papain was chosen for enzymatic hydrolysis and the degree of hydrolysis (DH) was selected as the evaluation standard. The optimal hydrolysis conditions were confirmed through one-factor-at-a-time study and response surface methodology. By using the enzyme-to-substrate ratio at 4.4%， the DH could reach 43.18% in 4 h at 70 ℃. Thereafter， cascade peptides (1 ku， 1-5 ku， and 5-10 ku) were isolated from hydrolysate using Pall Minimate ultrafiltration system and were evaluated as the superoxide radical (·O₂-) and hydroxy radical (·OH) scavengers. The antioxidant assays showed that the peptides of 1 ku molecular weight exhibited the best ·O₂- scavenging activity. Therefore， the hydrolysate of Aj sperm might be used as a potential antioxidant peptides source for nutraceutical， pharmaceutical and cosmetics industries.