A series of 3-arylidenamino-4-phenyl-4,5-dihydro-1H-1,2,4-triazol-5-ones N were obtained from the reaction of 3-amino-4-phenyl-45-dihydro-1H-1,2,4-triazol-5-one IVa with certain aldehydes. Compounds V were hydrogenated with NaBH, in diglyme to afford 3-alkylamino-4-phenyl-4,5-dihydro-1H-1,2,4-triazol-5-ones. VI. So, a general and convenient method was improved for the synthesis of type VI compounds. Eleven new and potential biologically active compounds were synthesized and characterized by elemental analyses, C-13-NMR, H-1-NMR, UV and IR spectra.