Novel side-chain-type sulfonated poly(arylene ether ketone) with pendant sulfoalkyl groups (SPAEK-xx) were synthesized by post-sulfonation method. Their structures were confirmed by FT-IR and NMR spectra. The all obtained membranes had excellent thermal stability and mechanical properties. The side-chain-type SPAEK films showed good dimensional stability, and their water uptake and swelling ratio were lower than those of the main-chain-type SPAEK with similar ion exchange capacity (IEC) value. It should be noted that the most highly sulfonated copolymer, SPAEK-100 (DS=1.0) with IEC of 1.54 meq./g, showed proton conductivity of 0.083 S/cm and water swelling ratio of only 9.74% at 80 degrees C. Moreover, the methanol permeability of SPAEK-100 membrane was 3.95 x 10(-7) cm(2)/s, which was much lower than 23.80 x 10(-7) cm(2)/s of Nafion 117. (C) 2009 Elsevier Ltd. All rights reserved.