A blend (Nafion/PVdF copolymer) membrane with high proton conductivity and low Nafion contents is prepared for the direct methanol fuel cell (DMFC). The composition in the blend membrane is fixed by the PVdF copolymer/Nafion ratio (80/20, w/w). The proton conductivity of the blend membrane is controlled by the pores in the membrane and by the solvents. The pores are generated by the phase separation in the blend membrane when acetone is used as a co-solvent. The pores enhance the proton conductivity of the blend membrane because they allow a much higher water uptake. The mechanical strength of the fully hydrated blend membrane can be sustained for DMFC applications because most of the water is captured in the pores by the strong hydrophobicity of PVdF. Moreover, the cell using the blend membrane (A8020) shows good performance because of the increased interfacial adhesion between the electrodes and the blend membrane. This result indicates that the blend membrane (PVdF/Nafion) has enhanced interfacial stability with the electrodes.