PURPOSE: To obtain an angiotensin I converting enzyme-inhibiting peptide reduced in side effects, its proper production and uses.

CONSTITUTION: The angiotensin I converting enzyme-inhibiting peptide has a structure of the formula Gly-Lys-Lys-Val-Leu-Gln, Phe-Gln-Lys-Val-Val-Ala-X (X is Gly, Lys, Ser or a group free of amino acid residue). This peptide is produced by separating from swine erythrocyte and purifying the separated peptide. This peptide can be produced also by a chemical synthesis. The peptide can be applied to various kinds of foods and medicines. Since Gly-Lys-Lys-Val- Leu-Gln and Phe-Gln-Lys-Val-Val-Ala-X (X is Gly, Lys, or a group free of amino acid residue) exhibits angiotensin I converting enzyme-inhibiting action, the peptide lowers blood pressure.