Partially sulfonated poly(ether sulfone) (SPES) was prepared and electrospun to bead-free nanofibers. The obtained data from solution conductivity measurements and scanning electron microscopy illustrated that sulfonation leads to a drastic increase in polymer solution conductivity and a considerable decrease in nanofiber diameter and a narrower diameter distribution. The new types of membranes were fabricated using Nafion-filled electrospun mats. The porous SPES nanofibrous membranes were impregnated with appropriate amount of Nafion solution. After a good pore-filling, an excess amount of Nafion solution was used to form a uniform top layer (SPES-N-N). Another bilayer polyelectrolyte membrane was prepared by direct electrospinning of SPES nanofibers on Nafion112 membrane's surface and followed by impregnation of Nafion solution into the pores of electrospun SPES (SPES-N-N112). The membranes were characterized by methanol permeability, proton conductivity, oxidative/hydrolytic stability as well as single cell direct methanol fuel cell (DMFC) performance tests. The proton to methanol selectivity of the SPES nanofiber-based bilayer membranes is about 53,680 and 45,500S s cm(-3) for SPES-N-N and SPES-N-N112 in comparison with 28,300 and 40,500S s cm(-3) for Nafion112 and Nafion117, respectively. The single cell DMFC performance results revealed that the SPES nanofiber-based-bilayer membranes have higher electrochemical performance than Nafion112 and Nafion117 membranes especially in elevated methanol concentration. The results showed that the fabricated bilayer membranes can be used as a promising polyelectrolyte membrane for fuel cell applications (C) 2010 Elsevier B.V. All rights reserved.