Organic/inorganic hybrid membrane with silica supported heteropoly acid was applied to reduce methanol cross-over with keeping ionic conductivity high for direct methanol fuel cells (DMFCs). In situ micro-emulsion impregnation of silica supported heteropoly acid into a proton exchange membrane (PEM), Nafion((R)), resulted in a homogeneous distribution of proton conducting inorganic networks in the hybrid membrane. The hybrid membranes showed 50-80% lower methanol cross-over than Nafion((R)) membrane, and DMFCs with them showed 10% higher fuel efficiency than that with Nafion((R)) membrane. The effects of lower methanol cross-over in the hybrid membrane were proven to be dominant in a highly concentrated fuel, and the hybrid membrane performed two times higher in the fuel efficiency compared with Nafion((R)) in 10 M methanol fuel. Also to achieve high fuel efficiency, the cathode recycling method was proposed and it performed 35% higher fuel efficiency than the cathode un-recycling method. (c) 2007 Elsevier B.V. All rights reserved.