The radical scavenging activity of several samples of ishiru , Japanese fish sauce made from fish or squid and mainly prepared in Ishikawa prefecture, was investigated. Ishiru made from squid (squid-ishiru ) showed significantly higher activity (1.70 mg of Trolox eq./g) than ishiru made from sardine, horse mackerel-added chub mackerel, and deep-sea smelt. Squid-ishiru also showed higher absorbance at 500 nm (the intensity of browning of ishiru ) and a greater content of total nitrogen than the other ishiru samples. The 70% ethanol extract of squid-ishiru was applied to Sephadex LH-20 gel filtration chromatography. Among the four peaks detected by the absorbance at 220 nm, peak 1 showed the highest radical-scavenging activity and was further purified by reversed-phase HPLC. Three peaks in the chromatogram showed even higher radical-scavenging activity, and a peptide was obtained from one of these peaks. Its sequence was (unidentified N-terminal)-Phe-Gly-Ser (or Phe)-Leu.