A novel crosslinked membrane is successfully prepared, composed of sulfonated poly(ether ether ketone) (sPEEK) as the acidic polymer and 4,4'-diaminodiphenylether (ODA) as the basic component, along with the aminated cross-linker. Being associated with the hydrogen bonds and electrostatic forces between the acidic and the basic groups, this membrane efficiently reduces water uptake. Accordingly, the dimensional stability of the electrolyte membrane under high humidity at elevated temperatures can be significantly improved. Cross-linking leads to a slight decrease in both methanol permeability and proton conductivity. However, by adjusting the cross-linking percent, the proton conductivity of all the composite membranes still maintained high values. In addition, even when dried out, the acid-base composite membrane exhibits good mechanical properties with high flexibility. The dimensional stability and selectivity of the acid-base composite membrane are better than those of sPEEK, leading to a better cell performance. As such, the acid-base composite membrane stands as a stable electrolyte membrane in direct methanol fuel cell (DMFC) system applicable at high temperature. (C) 2011 Elsevier B.V. All rights reserved.