An efficient sonochemistry methodology is described for the synthesis of 3, 4-dihydropyrimidin- 2(1H)-ones (Biginelli reaction) by condensation of various substituted benzaldehydes, Diketone/ β -ketoester and urea/ thiourea, at ambient temperatu re promoted by Chlorosulphonic acid (ClSO 3 H) under solvent-free condition. This method gives the desired dihydropyrimidines in excellent yields in short reaction time at ambient temperature.