In this work, we prepared crosslinked poly(vinyl alcohol) (PVA) nano-fiber thin film by electro-spinning from a PVA aqueous solution and then treating the electro-spun fiber film with glutaraldehyde vapor to start crosslinking reaction. The crosslinked PVA nano-fiber thin film is impregnated in a Nafion solution to prepare Nafion/PVA-fiber composite membranes. We show that the optimum PVA content of Nafion/PVA-fiber membrane is similar to 10 wt%, which is higher than the 5 wt% PVA content of Nafion/PVA blend membrane reported by DeLuca and Elabd. The introduction of 10 wt% crosslinked PVA nano-fiber in a Nafion membrane allows us to reduce the thickness of the Nafion/PVA-fiber membrane (thickness similar to 50 mu m) to less than 1/3 of that of Nafion-117 membrane (thickness similar to 175 mu m) and DeLuca and Elabd's Nafion/5 wt% PVA blend membrane (thickness 181 mu m) without causing large increment of methanol crossover across the membrane. However, the smaller thickness of Nafion/PVA-fiber membrane causes it to have lower proton resistance than Nafion-117 and Nafion/PVA blend membranes. We show that the Nafion/PVA-fiber membrane consisting of 10 wt% crosslinked PVA nano-fiber has a better DMFC performance than Nafion-117 and Nafion/5 wt% PVA blend membranes. (C) 2010 Elsevier B.V. All rights reserved.