In the present study, modified acid-base blend membranes were fabricated via incorporation of sulfortated poly(arylene ether benzimidazole) (SPAEBI) into sulfonated poly(arylene ether sulfone) (SPAES). These membranes had excellent methanol-banier properties in addition to an ability to compensate for the loss of proton conductivity that typically occurs in general acid-base blend system. To fabricate the membranes, SPAEBIs, which served as amphiphilic polymers with different degrees of sulfonation (0-50mol%), were synthesized by polycondensation and added to SPAES. It resulted in the formation of acid-amphiphilic complexes such as [PAES-SO3](-) (+)[H-SPAEBI] through the ionic crosslinking, which prevented SO3H groups in the complex from transporting free protons in an aqueous medium, contributing to a reduction of ion exchange capacity values and water uptake in the blend membranes, and leading to lower methanol permeability in a water-methanol mixture. Unfortunately, the ionic bonding formation was accompanied by a decrease of bound water content and proton conductivity, although the latter problem was solved to some extent by the incorporation of additional SO3H groups in SPAEBI. In the SPAES-SPAEBI blend membranes, enhancement of proton conductivity and methanol-barrier property was prominent at temperatures over 90 degrees C. The direct methanol fuel cell (DMFC) performance, which was based on SPAES-SPAEBI-50-5, was 1.2 times higher than that of Nafion (R) 117 under the same operating condition. (C) 2007 Published by Elsevier B.V.