Abstract: There are provided novel aminophosphonic acid derivatives of the general formula [I]: ##STR1## wherein n is an integer of 2 or 3; R.sup.1 is a phenyl, naphthyl, indolyl, benzothienyl, benzofuryl or benzoxazolyl group which may have 1 to 3 substituents selected from the group consisting of hydroxyl and lower alkyloxy groups, or a hydrogen atom; R.sup.2 is a lower alkyl group, a benzyl group, a 4-hydroxybenzyl group, a 3-indolylmethyl group or a .beta.-phenethyl group; and A is an optional residue of an amino acid selected from the group consisting of tryptophane, tyrosine, phenylalanine, homophenylalanine, naphthylalanine or N.sup..omega. -nitroarginine, and their pharmaceutically acceptable salts. The compounds according to the present invention and their pharmaceutically acceptable salts exhibit an inhibitory activity against endothelin-converting enzyme, and are expected to be useful as a drug treating various diseases with which endothelin is concerned.