To suppress methanol crossover in direct methanol fuel cells (DMFCs), a Nafion-Bi2V0.75Sb0.25O5.4 composite membrane was prepared by recast method. Oxygen-ion conductive Bi2V0.75Sb0.25O5.4 powders were highly dispersed in a Nafion 117 membrane to physically block methanol crossover and/or chemically oxidize the methanol, which was confirmed by the difference in the methanol diffusion coefficient between recast Nafion and Nafion-Bi2V0.75Sb0.25O5.4 composite membranes. Interestingly, mixing 20 wt % Bi2V0.75Sb0.25O5.4 into Nafion 117 membrane largely suppressed the methanol crossover, but only slightly decreased the proton conductivity of the membrane, resulting in a large improvement in the DMFC performance. The stabilities of Bi2V0.75Sb0.25O5.4 in 5% Nafion solution, water, and 1 M H2SO4 were measured using an inductively coupled plasma atomic emission spectrometer, and the electrochemical stability of Bi2V0.75Sb0.25O5.4 in 1 M H2SO4 solution was obtained using cyclic voltammetry. The oxygen-ion conductivities of Bi2V0.75Sb0.25O5.4 at temperature ranges from 80 to 400 degrees C were also measured. (c) 2006 The Electrochemical Society.