We purified a novel angiotensin-I converting enzyme (ACE) inhibitor from fish sauce Ishiru prepared from squid, and identified it as the tripeptide Leu-Ala-Arg (LAR). IC50 of this ACE inhibitor was 2.5 μM, demonstrating high potency among peptides previously purified from fish sauces. Moreover, LAR acted as an antihypertensive peptide, reducing systolic blood pressure in spontaneously hypertensive rats.