The porous polyimide films were prepared by a wet phase inversion process. The influence of coagulating non-solvent on morphology, pore size and porosity of porous films was investigated. A series of pore-filling sulfonated polyimide (PFSPI) membranes, which derived from a homogenous spongy-like porous polyimide film as matrix filled with sulfonated copolyimides, were prepared and characterized. These PFSPI membranes exhibited excellent thermal stability with desulfonation temperature of 283-330 degrees C and good oxidative stability in Fenton's agent due to the protective effect of porous polyimide matrix on the sulfonic acid groups. The swelling of PFSPI membranes could be effectively suppressed by the porous matrix, which leads to the excellent dimensional stability and good water stability of membranes. The PFSPI membranes exhibited high proton conductivity at elevated temperature. All the PFSPI membranes displayed better permselectivity as compared with Nafion 115, which is attributed to their much lower methanol permeability. (C) 2012 Elsevier Ltd. All rights reserved.