New preparation procedures of Ru-Sn/Y zeolite catalysts for acetic acid (methyl acetate) formation from methanol alone in the heterogeneous gas-solid phase were investigated. The catalysts were prepared with the following three procedures: (i) the evacuation of [Ru(NH3)(6)](3+)/Y to form Ru-metal particles in the zeolite cavities (ii) the reaction of Cl-2 gas and Ru-metal particles to form RuCln species in the cavities and (iii) introducing SnCl2 as a vapor, The methanol conversion at 473 K gave methyl acetate and hydrogen after a characteristic induction period. Stationary activity was sustained with a slight decrease until 200 h from the reaction start. The yield of methyl acetate was dependent on the conditions of the Cl-2 and Sn treatment, and reached up to 10.9% with the catalyst prepared under the optimum condition. The characterization results of the catalyst at each preparation and reaction stage suggested that the active species were formed during the induction period in the supercages of the zeolites and were Ru-m-Sn-n species.