Blend membranes consisting of sulfonated poly(ether ether ketone) (SPEEK), which is an acidic polymer, and polysulfone bearing benzimidazole side groups (PSf-BIm), which is a basic polymer, have been prepared with various PSf-BIm contents (0 - 10 wt%). The blend membranes have been characterized by ion exchange capacity, proton conductivity, liquid uptake, methanol permeability, and polarization measurements in direct methanol fuel cell (DMFC). The membranes with an optimum PSf-BIm content of similar to 8 wt% exhibit electrochemical performance in DMFC better than that of plain SPEEK membrane due to an enhancement in proton conductivity through acid-base interactions and lower methanol crossover. (c) 2007 The Electrochemical Society.