The purpose of the present work is the development of new multiphase polymer electrolyte membranes substituting Nafion. To reduce the methanol permeability and the cost of the current Nafion membranes, sulfonated hydrocarbon membranes of polysulfone and polyether ketone were blended with nonsulfonated and hydrophobic polysulfone or polyether ketone. The sulfonated phase will act as the proton conducting phase and the nonsulfonated, hydrophobic phase acts as the methanol barrier. By forming the spinodal (co-continuous) morphology through controlling the phase separation kinetics during the casting of the membranes, the continuous hydrophobic phase will restrict the swelling of the neighboring hydrophilic phase (the proton conducting phase) and thus reducing the methanol cross-over through the free water in the hydrophilic conducting phase. Semi-IPN's of crosslinked sulfonated polysufone and nonsulfonated polysulfone membranes were also evaluated as the multiphase polymer membranes for direct methanol fuel cell.