L-Tyr-L-Val, L-Leu-L-Tyr, L-Leu-L-Pro, L-Phe-L-Tyr, L-Tyr-L-Arg and its acid addition salts, L-Leu-L-Ser-L-Pro, L-Leu-L-Gln-L-Pro, L-Phe-L-Leu-L-Pro, L-Leu-L-Leu-L-Pro, L-Leu-L-Asn-L-Pro, L-Phe-L-Pro, L-Leu-L-Ala-L-Ala, L-Val-L-Ala-L-Ala, L-Leu-L-Gln-L-Gln, L-Val-L-Ala-L-Tyr, L-Leu-L-Ala-L-Tyr, L-Leu-L-Ser-L-His and its acid solution salts, L-Ile-L-Arg-L-Ala and its acid addition salts, L-Leu-L-Arg-L-Pro and its acid addition salts, and L-Ile-L-Arg-L-Ala-L-Gln-L-Gln and its acid addition salts, derived from a corn protein .alpha.-zein, and tripeptides represented by the formulaL-(or D-) Leu-L-X.sub.aa -L-Prowherein X.sub.aa is Gly, Ala, Val, Ile, Thr, Asp, Glu, Lys, Orn, Cys, Met, Phe, Tyr, Trp, His or a hydroxyproline residue, pharmacologically acceptable acid addition salts of the above tripeptides wherein X.sub.aa is Lys, Orn, His or Arg, and pharmacologically acceptable alkali or alkaline earth metal salts, ammonium salts or organic base salts of the tripeptides wherein X.sub.aa is Asp or Glu, have an angiotensin converting enzyme-inhibiting activity.