Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion 15 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity. methanol permeability and cell performance. The proton conductivity was slightly decreased by 1-3% compared with Nafion 115, which still kept the high proton conduction of Nafion 115. The methanol permeability of Nafion/PI-PVA-TSPS composite membranes was remarkably reduced by 35-55% compared with Nafion 115. The power density of DMFCs with Nafion/PI-PVA-TSPS composite membranes reached to 100 mW/cm(2), exceeding that with Nafion 115 (68m W/cm(2)). (C) 2009 Elsevier Ltd. All rights reserved.