Sulfonated polysulfone (SPSU) with high ion exchange capacity (lEC) and ion conductivity was synthesized through deep sulfonation of polysulfone using the trimethysilyl chlorosulfonate as sulfonation agent. The silicon-containing compounds formed during the synthesis of SPSU were completely removed from the SPSU by simple evaporation. Water swelling, ion exchange capacity, conductivity and fuel cell performance were measured for the SPSU membranes. SPSU membranes with IEC twice that of Nafion- 115 were prepared. The conductivity of the SPSU increased exponentially with the relative humidity (RH), achieving conductivities Of 0.1 S cm(-1) for RH > 70%. A Nafion-layered SPSU PEM fuel cell membrane was synthesized through pressing a thin Nation-115 layer on to both sides of SPSU membrane. The Nafion layers on the SPSU prevented the water-soluble SPSU from being washed out of MEA, and the membrane was stable during the fuel cell operation up to 120 degrees C. (c) 2005 Elsevier B.V. All rights reserved.