For the purpose to examine as to their antiviral activities, 2-acylaminoacetamidine (II) and 3-acylaminopropionamidine hydrochlorides (III) were synthesized from the corresponding nitriles via ethyl imidates. The difference of the reactivity between ethyl 2-acylaminoacetimidates and ethyl 3-acylaminopropionimidates on the course of amidination were postulated. Iminoesterification of dinitrile, (p-cyano) benzamidopropionitrile (XVIII), was discussed by referring the infrared spectrum of a corresponding monocyanomonoester, ethyl p-(N-cyanoethylcarbamoyl) benzoate (XXI). Among the compounds obtained hereof, 3-(p-methyl) benzamidopropionamidine hydrochloride was found to have an inhibitory effect on influenza virus in mice and in membrane culture.