Sulfonated poly(arylene thioether phosphine oxide)s (sPATPO) with high ion exchange capacity generally shows excessive swelling, hampering their application as proton exchange membranes. To reduce their swelling, they were blended with sulfonated benzimidazoles (sPBIs) because they could form strong intermolecular interactions with sPBIs. Such sulfonated benzimidazoles should exhibit excellent solubility so as to prevent the formation of precipitate during the blend process. In order to achieve sPBI with high solubility, high content hexafluoroisopropylidene moieties were incorporated into the polymer backbone by polycondensation. The sPATPO/sPBI blend membranes present high thermal stability. More importantly, they show low swelling while maintaining high proton conductivity. At the same time, their oxidative stability is remarkably increased and their mechanical properties are also improved. As a result, these blend membranes indicate excellent comprehensive properties. (C) 2011 Elsevier B.V. All rights reserved.