We successfully synthesized porous co-polyimide membranes from a polycondensation reaction of an aromatic dianhydride of 3,3',4,4'-biphenyltetracarboxylicdianhydride (SBPDA) with diamines of p-phenylenediamine (PPDA) and 4,4'-oxydianiline (ODA) by a wet phase inversion process. Factors affecting the mechanical strength of the membrane and porosity were discussed. By tuning the parameters, a spongy type porous membrane with high mechanical strength and high porosity was obtained. In addition, the porous co-polyimide membrane consisted of a porous top layer and a spongy type sub-structure. This material is suitable as the matrix of a multifunctional composite membrane of a direct methanol fuel cell (DMFC) by filling protonic electrolytes in the micropores of the matrix. (c) 2009 Elsevier B.V. All rights reserved.