The preparation of substituted benzoylamino acids and mercaptoacylariaino acids as inhibitors of angiotensin converting enzyme is described. The bulky phenyl ring directly attacted to an amino acid as of benzoylamino acid seemed unsuitable for the inhibitory activities. Among the mercaptosuccinylamino acids, _L-proline was more favorable than _L-phenylalanine while S-acetylation was unfavorable.