The problem of methanol crossover through Nation membranes is one of the challenges in the application of direct methanol fuel cells (DMFCs). In order to reduce methanol crossover, the Nation membrane is modified by sputtering a thin layer of Pt/Pd-Ag/Pt on its surface in the present study. The modified membrane was characterized using scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD), and time-of-flight secondary ion mass spectroscope system (TOF-SIMS). The characterization indicates that sputtering over the surface of Nafion polymer can successfully form an alloy layer of Pt/Pd-Ag/Pt although it is not crack-free. In applying the modified membrane (Pt/Pd-Ag/Pt/Nafion) to a 5 cm(2) single cell of DMFC, it is found that this new membrane is effective in reducing methanol crossover in the cell and gives a higher cell performance than that of a single Nation membrane. Among the three modified Nation 117 membranes having 0.1, 0.2, and 1 mum of sputtering Pd-Ag film, the 1 mum thick film gives the highest performance. The results also show that the performance of the fuel cell with 1 mum sputtering Pd-Ag film on the Nation membrane is higher than that of cell with Nation membrane having catalyst loading twice as high. (C) 2003 Elsevier Science B.V. All rights reserved.