Novel polymer composite membranes composed of sulfonated polyarylenethioether sulfone (SPTES) and sulfonated polybenzimidazole (SPBI) were prepared by solution casting with the composition of SPTES in the varied range from 30 to 70 wt%. The proton conductivity of the composite membranes was measured by four probe impedance spectroscopy at different temperatures. The highest proton conductivity (up to 100 mS/cm) was found for the SPTES/SPBI (70/30) polymer composite membrane at 85 degrees C, 85% relative humidity, and proton conductivity increased when the SPTES content increased. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) were used to confirm the presence of SPBI in the composite membranes as well as the dispersion of SPBI The results indicated that membranes showed a good perspective as proton exchange membrane (PEM) for fuel cell applications. (c) 2007 Elsevier B.V. All rights reserved.