Abstract: The ovary of Japanese seallop(Patinopecten yessoensis) was hydrolyzed for protein powder rich in polypeptides. The concentration of the remaining oxygen and the elimination of DPPH free radicals were determined. The results showed that there was 87.92% of protein in the hydrolyzate. The hydrolyzate with 10 g/L had 61.68% of the eliminating activity of DPPH free radical.