Composite membranes were fabricated consisting of aligned domains of Nafion (R) 1100 surrounded by a supporting matrix of polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SEBS). The structure of the composite was controlled via the application of an electric field during solvent casting. Nafion (R) domains were aligned across the membrane thickness to provide paths for proton conduction. The surrounding SEBS domain limits methanol permeability. Compared to randomly structured Nafion (R)/SEBS composites, the membranes with field-aligned domains display significantly enhanced performance in direct methanol fuel cells (DMFCs). The membranes with field-aligned domains display DMFC performance better than commercial Nafion (R) 117 membranes under high methanol fuel concentration. (C) 2009 Elsevier B.V. All rights reserved.