The composite membranes were prepared by impregnation of porous poly(tetrafluoroethylene) (PTFE) membranes with Nation solutions containing various contents of surfactant Triton(R) X-100 (polyethylene glycol tert-octylphenyl ether). Dynamic light scattering (DLS) was used to investigate the polymer aggregations sizes distributions of Nafion solutions. The scanning electron microscope (SEM) and energy dispersion X-ray (EDX) analyzer were used to study the morphology of the surface of composite membranes. The experimental results revealed that mixing 1-3wt.% of Triton(R) X-100 into the Nafion solutions causes the dissociation of Nation aggregations in the solutions. Thus, the Nafion molecules are easy to penetrate into the pores of PTFE membranes, leading to a better ionic conductivity and lower gas permeability of composite membranes. (C) 2004 Elsevier B.V. All rights reserved.