An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives using formic acid as catalyst, from aldehydes, beta-ketoester and urea(thiourea) without solvent under the irradiation of microwave is described. Compared with the classical Biginelli reaction, this new method has the advantage of good yields (77-94% for aromatic aldehydes) and short reaction time (3-8 min). (C) 2007 Qi Dong You. Published by Elsevier B.V. on behalf of Chinese hemical Society. All rights reserved.