The control of the mesoporous structure in a carbon membrane from a poly(ethylene glycol)/polyimide-blended polymer was investigated. The size of the pores tends to become large with increase of the content of poly(ethylene glycol) against polyimide, that is, the mesoporous structure could be controlled by the composition of the blended polymers. On the other hand, the average molecular weight; of poly(ethylene glycol) has little effect from the viewpoint of the control of the pore structure.