To identify the antioxidative peptides in the gelatin hydrolysate of bovine skin, the gelatin was hydrolyzed with serial digestions in the order of Alcalase, pronase E, and collagenase using a three-step recycling membrane reactor. The second enzymatic hydrolysate (hydrolyzed with pronase E) was composed of peptides ranging from 1.5 to 4.5 kDa, and showed the highest antioxidative activity, as determined by the thiobarbituric acid method. Three different peptides were purified from the second hydrolysate using consecutive chromatographic methods. This included gel filtration on a Sephadex G-25 column, ion-exchange chromatography on a SP-Sephadex C-25 column, and high-performance liquid chromatography on an octadecylsilane chloride column. The isolated peptides were composed of 9 or 10 amino acid residues. They are: Gly-Glu-Hyp-Gly-Pro-Hyp-Gly-Ala-Hyp (PI), Gly-ProHyp-Gly-Pro-Hyp-Gly-Pro-Hyp-Gly (PII), and Gly-ProHyp-Gly-Pro-Hyp-Gly-Pro-Hyp (PIII), as characterized by Edman degradation and fast-atom bombardment mass spectrometry. The antioxidative activities of the purified peptides were measured using the thiobarbituric acid method, and the cell viability with a methylthiazol tetrazolium assay The results showed that PII had potent antioxidative activity on peroxidation of linoleic acid. Moreover, the cell viability of cultured liver cells was significantly enhanced by the addition of the peptide. These results suggest that the purified peptide, PII, from the gelatin hydrolysate of bovine skin is a natural antioxidant, which has potent antioxidative activity.