Sulfonated PEEK-WC polymer was obtained according to chloro-sulfonic acid procedure maldng possible the preparation of different membrane samples with a sulfonation degree from 48 to 90%. Dense membranes were prepared from casting solutions of S-PEEK-WC dissolved in DMF. Proton conductivity measurements were performed on such S-PEEK-WC membranes in a range of temperature from 30 to 120 degrees C and 100% of relative humidity, reaching 2.5 x 10(-2) S cm(-1) as the best value at 100 degrees C and with a sulfonation degree of 90%. In the meanwhile, the open circuit voltage of this S-PEEK-WC membrane (DS = 90%) varied from 0.963 V at 60 degrees C to 0.802 V at 100 degrees C, demonstrating that an increase of temperature negatively affects the membrane performance due to the mechanical properties degradation. In this work, a wide experimental campaign was carried out to investigate the electrochemical performances in terms of polarization curves, open circuit voltage and proton conductivity of S-PEEK-WC membranes as well as the fuel crossover and water uptake. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.