A peptidic fraction having antioxidant activity was separated from the proteolytic digest of dried bonito protein by ion-exchange chromatography and gel filration. Further separation by ODS HPLC afforded eleven active peptides; Val-Lys-Leu, Val-Val-Lys-Leu, Val-Lys-Val, Pro-Lys-Ala-Val, Ile-Lys-Leu, Val-Pro-Ser-Gly-Lys, Glu-Ala-Lys, Phe-Val-Ala-Gly-Lys, Lys-Ala-Ile, Lys-Val-Ile, and Lys-Asp. The structure-activity relationship of these peptides was discussed.