The durability of a novel Nafion/poly(tetrafluoroethylene) (PTFE) composite membrane was evaluated using an accelerated stress test. The composite membrane was embedded with a porous PTFE layer and was prepared by the solution-casting method using 5% Nafion solution. The porous PTFE layer was treated chemically to improve its hydrophilicity before incorporating it within the membrane. The goal of the hydrophilic treatment was to improve the interfacial bonding between the Nafion polymer and the PTFE fibers resulting in improved strength and durability. The accelerated degradation testing was performed by the wet/dry gas cycling method. The chemical and mechanical stability of the membrane was evaluated by measuring the polarization curve, hydrogen crossover, and proton resistance during wet/dry cycles. Cross-sections of the composite membrane were examined after failure by a scanning electron microscope. The results show that the degradation rate of the composite fuel cell membrane incorporating the PTFE layer with hydrophilic pretreatment was lower than the degradation rate of the membrane with untreated PTFE. Tensile testing revealed that the composite membrane with pretreated PTFE has higher mechanical strength compared to both the composite membrane with untreated PTFE, and a commercial Nafion membrane. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.016301jes] All rights reserved.