Abstract: In the presence of benzene as solvent, the ammonium S-alkyl ethyl-phosphonotrithioates were prepared by reaction of the ethylthionophosphine sulfide with mercaptans for 6-8 hrs, and then into which the dried ammonia gas was introduced.Through the reaction between those above ammonium salts and N-substituted a-chloroacetylamide, we obtained twelve S-alkyl-S-(N-substituted carbamoyl-methyl) ethylphosphono-trithionates. But, we could not obtain the products by means of the sodium salts instead of the ammonium salts.