Abstract: The present invention provides a cyanoguanidine derivtive which is a precursor for the synthesis of N-cyano-N'-methyl-N"-[2-{(5-methyl-1H-imidazol-4-yl)methylothio}ethyl]-gua nidine (Cimetidine) or its relted compound, which has an action of controlling secretion of acid in the stomach based on the histamine H.sub.2 receptor antagonism and is valuable as a drug for treating gastric ulcer. This cyanoguanidine derivative is prepared by reacting a haloketone derivative with an ammonium salt and a lower fatty acid salt or by reacting other cyanoguanidine derivative with an ammonium salt.