Synthesis of cesium-substituted dodecatungstophosphoric acid (Cs2.5H0.5PW12O40) supported on K-10 clay is reported. The catalyst is fully characterized. It serves as a promising catalyst for the acylation of aromatic compounds. The acylation of anisole with benzoyl chloride was studied systematically by using 20% w/w Cs2.5H0.5PW12O40/K-10 and this catalyst can be reused without any further chemical treatment, eliminating the effluent disposal problem. This acylation reaction is 100% selective toward 4-methoxybenzophenone, which is the desired perfumery intermediate. The effect of various important kinetic parameters was evaluated systematically to establish that the reaction obeys the Eley-Rideal type of mechanism with a very weak adsorption of the reactants. The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically controlled. (C) 2003 Elsevier Science (USA). All rights reserved.