The direct carbonylation of methanol, without any halide in the feed as a promoter, ispresented. A series of Mo catalysts supported on activated carbon, γ-Al2O3 and SiO2 were prepared.The results show that the support greatly affects the Mo catalyst in the direct vapor-phase carbonylationof methanol, and activated carbon is the best supports of the investigated supports. In addition, therelationships between adsorptions of NH3 and CO and carbonylation of methanol were investigated. A novelsulfided Mo/C catalyst had high activity and selectivity for the vapor phase carbonylation of methanol tomethyl acetate without the addition ofa CH3I promoter to the feed. The reaction conditions were optimizedat a reaction temperature of 573 K, a methanol concentration of 23 mol% and a carbon monoxide spacevelocity of 3,000 L/(kg.h). Under these optimal conditions a methanol conversion of 50%, carbonylationselectivity of 80 mol%, and space-time yield of 8.0 mol/(kg.h) were obtained. The active phase of thisnovel sulfided Mo/C catalyst is the non-crystalline phase, and the active component is present as MoS2.5on the surface of the activated carbon.