Sulfonated polystyrene-block-poly(ethyl-ran-propylene)-block-polystyrene (S-polySEPS) was synthesized by sulfonation at the phenyl groups of polySEPS with the various concentrations of chlorosulfonic acid (CSA). The proton conductivity of the S-polySEPS films was ranged from 10(-2) to 10(-1) S/cm. In particular, the S-polySEPS film prepared with polySEPS/CSA (molar ratio, 1.0/1.0) has the best proton conductivity (1.36 x 10(-1) S/cm) and water uptake (68%) at 90 degrees C. Most of the S-polySEPS films have higher proton conductivity and water content than Nafion (R) 117 at the considering temperature range. The IEC value of the films was improved with increasing the concentration of ionic groups. The TEM image shows that micro-phase separated channels were comprised of ionic-segments displayed within polySEPS matrix. The size of dark ionic channels was about 5-12 nm. The H-1 NMR and FT-IR analysis was used to verify the sulfonation of polySEPS. The TGA was carried out to investigate the thermal stability of the S-polySEPS films. The current density of the S-polySEPS film (1100 mA/cm(2)) prepared with polySEPS/CSA (molar ratio, 1.0/1.0) was higher than that of the Nafion (R) 117 (680 mA/cm(2)) at 0.7 V. (c) 2013 Elsevier B.V. All rights reserved.