Dimethyl carbonate (DMC) synthesis reaction by oxidative carbonylation of methanol has been studied using vapor phase flow reaction system in the presence of Cu-based catalysts. A series of Cu-based catalysts were prepared by the conventional impregnation method using activated carbon (AC) as support. The effect of various promoters and reaction conditions on the catalytic reactivities were intensively evaluated in terms of methanol conversion and DMC selectivity. The morphological analysis by X-ray diffraction and SEM was also conducted in order to characterize the emloyed catalysts. Regardless of catalyst compositions, the optimal reaction temperature for oxidative carbonylation of methanol was found to be around 120-130 degreesC. The reaction rate was too slow below 100 degreesC, while too much by-products was produced above 150 degreesC. Among the various catalysts employed, CuCl2/NaOH/AC catalyst with the molar ratio of OH/Cu = 0.5-1.0, has shown the best catalytic performance, which appears to have a strong relationship with the formation of intermediate species, Cu-2(OH)(3)Cl.