5-Benzylidene-, 5-(furan-2-ylmethylene)- and 5-(thiophen-2-ylmethylene)-4,5-dihydro-1,2,4-triazin-6-ones have been synthesized from the reaction of 4,5-dihydro-1,2,4-triazin-6-ones with appropriate aromatic aldehydes. All the products have been characterized by elemental analysis and their spectral data.