The vapor-phase MTBE decomposition was examined in a shell and tube-type catalytic membrane reactor (CMR). 12- Tungstophosphoric acid(PW) was used as a catalyst and poly-2,6-dimethyl-1,4-phenylene oxide (PPO) was used as a polymer material. A single-phase CMR (PW-PPO/Al₂O₃, type-1) and a composite CMR(PW-PPO/PPO/Al₂O₃, type-2) were successfully designed and characterized. It was revealed that the single-phase PW-PPO/Al₂O₃ showed perm-selectivities for reaction products. The selective removal of methanol through the catalytic membrane shifted the chemical equilibrium toward the favorable direction in the MTBE decomposition. The PW-PPO/PPO/Al₂O₃ showed the better preformance than PW-PPO/Al₂O₃. The enhanced performance of PW-PPO/PPO/Al₂O₃ CMR was due to the intrinsic perm-selectivity of PW-PPO and the additional separation capability of sub-layered PPO membrane.