Blend membranes consisting of sulfonated poly(ether ether ketone) (SPEEK, an acidic polymer) and various amounts of 1H-perimidine tethered polysulfone (a basic polymer) have been prepared and characterized. The blend membranes show increased proton conductivity and decreased ion-exchange capacity and liquid uptake in water and methanol/water solutions compared to plain SPEEK. The blend membranes also exhibit better electrochemical performance and lower methanol crossover in direct methanol fuel cells compared to plain SPEEK and Nafion 115 membranes due to an enhancement in proton conductivity through acid-base interactions and an insertion of the 1H-perimidine groups into the ionic clusters of SPEEK. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3243465] All rights reserved.