A series of novel branched sulfonated poly(ether ether ketone)s containing propenyl groups have been synthesized using a nucleophilic polycondensation reaction. Subsequently, a thiol-ene click chemistry reaction between propenyl and thiol groups results in a new series of copolymers containing benzimidazole sulfonic acid groups. The expected structures of the copolymers are confirmed by H-1 NMR and Fourier transform infrared spectroscopy. The introduction of benzimidazole sulfonic acid groups into the copolymer improves proton conductivity obviously. Compared with the linear sulfonated poly(ether ether ketone)s with the same sulfonation degree (DS), the BSPEEK-BIS membranes show lower water uptake and methanol permeability. The branching structure and the interaction between sulfonic acid and benzimidazole groups make the contribution to the improvement of the membrane's properties. Therefore, the high proton conduction, low methanol permeation, and low water uptake property of the as-prepared membranes are of significant interest for DMFCs. Crown Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.