The synthesis of dimethyl carbonate (DMC) from methanol, propylene oxide (PO) and carbon dioxide (CO2) over supported catalysts was studied for the first time. A series of supported solid base catalysts were prepared by impregnation and their catalytic activities were evaluated. It was found that KOH/4A molecular sieve was the most effective catalyst. The effects of various conditions. such as reaction time, reaction temperature, molar ratio of the reactants and KOH loading, on the yield of DMC was investigated. It was proposed that DMC was formed from the transesterification of propylene carbonate (PC) with methanol, where PC was synthesized from PO and carbon dioxide. Methanol was favorable to such cycloaddition of PO with CO2. Under the optimized conditions. PO was converted completely and the yield of DNIC was up to 16.8%. (C) 2004 Elsevier B.V. All rights reserved.