In order to isolate basic peptides having the inhibitory activities against Angiotensin I-con-verting enzyme (ACE) we investigated the enzymatically hydrolyzed products of sardine and hair tail meat. The concentration of purified basic peptides providing 50% inhibition was 39.7mg/100ml for sardine and 90.1mg/100ml for hair tail. Molecular weights of the basic peptides from both species by high performance liquid chromatography were 1000-2000. Amino acid analysis showed that the basic peptides contained such a large quantity of lysine as 47.68g/100g for sardine and 59.65g/100g for hair tail.