Composite membranes were fabricated consisting of aligned domains of Nafion® 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® 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®/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® 117 membranes under high methanol fuel concentration.