Conjugated cis/trans isomer-based polymer membranes were prepared with 15-25 mol% of bis(4-hydroxypheny1)-1,2-diphenylethylene (BHDPE). BHDPE has a conjugated nonplanar conformation structure containing the peripheral four aromatic rings which facilitate the formation of pi-pi interactions. A series of sulfonated poly(ethersulfone)s (S-PBHDPE) was synthesized with concentrated sulfuric acid. The sulfonation took place selectively on the BHDPE unit, and simultaneously on the side-chain and main-chain phenyl groups. The S-PBHDPEs consisted of a 4:6 ratio of cis and trans form mixtures. The S-PBHDPE membrane structures and characteristics were evaluated by H-1 NMR spectroscopy, and their thermal stabilities evaluated. The ion exchange capacity (IEC), water uptake (WU) and proton conductivity of the membranes were evaluated as a function of the molar percentage of the sulfonic acid group. The WU of the synthesized S-PBHDPE membranes ranged from 21 to 52%, compared with 28% for Nafion 211 (R). The S-PBHDPE membranes exhibited proton conductivities (80 degrees C, RH100) of 42.7-125.6 mS/cm, compared with 137.4 mS/cm for Nafion 211 (R). The surface morphologies of S-PES 40 and S-PBHDPE 20 membranes were studied by AFM images. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.