Flexible bi-continuous mesostructured polymer/inorganic composite membranes have been synthesized by undertaking co-assemblies of surfactants and inorganic sol-gel processes inside pores of a preformed porous polymer membrane such as PP porous membrane Celgard((R)) 2400. The pores are interconnected across the membranes, therefore the continuity of the inorganic mesopores across the membranes is guaranteed in principle. The solvent ethanol used for silica sot is conducive to the synthesis of inorganic materials such as silica within the pores although the PP membrane is hydrophobic. The composite membranes show new properties such as transparency, flexibility, uniform nanosized pores and enhanced permeability. (c) 2007 Elsevier Ltd. All rights reserved.