The performance of direct methanol fuel cells (DMFC) with radiation grafted polymer electrolyte membranes (PEM) is reported. The membranes used poly ethylene-tetrafluoroethylene (ETFE), poly vinylidene fluoride (PVDF) and low-density polyethylene (LDPE) as base polymer films. The base polymer films were grafted with polystyrene sulfonic acid (PSSA) as proton-conducting groups. The effects of varying the degree of grafting (DOG) and the membrane thickness, which change the ion conductivity and methanol permeability, has a strong influence on methanol crossover of the DMFC and the performance of the DMFC. Typically, increasing the degree of grafting increases the ion conductivity and the methanol crossover. By adjusting the degree of grafting and the membrane thickness, membranes with suitable conductivity and low methanol crossover have been produced. The DMFC performance with such membranes was superior to that of with Nafion((R)) membrane. (c) 2004 Elsevier B.V. All rights reserved.