Microwave-assisted synthesis of 4-methyl-2,3-dihydro-1H-1,5-benzodiazepin-2-one by the condensation of 1,2-phenylene-diamine and ethyl acetoacetate was examined. The yields were compared with those by classical heating under various conditions. The yield is mainly determined by the temperature of the reaction mixtures, and little affected by the difference in the heating methods. Nonthermal effects in microwave heating have not been observed.