The effect of casting solvent on the morphology of sulfonated polystyrene-block-poly(ethylene-ran-butylene) block-polystyrene (SSEBS) was investigated using transmission electron microscopy and small-angle X-ray scattering. Proton conductivities and methanol permeabilities were measured and the related impact on morphological changes is discussed. SSEBS is transformed from a well-ordered lamellar to a disorder structure as the concentration of MeOH in MeOH/THF mixtures increases.