We hydrolyzed pearl oyster meat with alkaline protease treatment. We administered orally hydrolysate of pearl oyster meat to 8 week-old male SHR/Izm. As a result, the systolic blood pressure of SHR fell significantly from our last quotation of 202.4 mmHg to 180.0 mmHg in six hours. We controlled, isolated and identified four kinds of physiologically active peptides with low molecular weight and high level of ACE inhibition, and refined and identified them as Phe-Tyr, Ala-Trp, Val-Trp, and Gly-Trp with reversed phase chromatography. Among them, Ala-Trp was new and naturally occurring peptide. We estimated that the percentage contributing to ACE inhibition by those four peptides is 4.5%. Based on the study, we believe that promote pearl oyster meat as nutritious and functional food reduces blood pressure.