Methanol crossover through the proton exchange membrane from the anode to the cathode is a major obstacle for the development of the direct methanol fuel cells (DMFCs). This work focuses on the exploration of a novel methanol-blocking membrane prepared by layer-by-layer assembly of poly(diallyldimethylammonium chloride) (PDDA) and graphene oxide (GO) nanosheets onto the surface of Nafion (R) membrane. Results demonstrate that the bilayers are methanol-blocking, which formed a dense and uniform thin film structure on the surface of Nafion (R) film. The methanol permeability measurement across the composite membrane shows a decrease in methanol diffusion coefficient by 67% in comparison to the pristine membrane. The limiting current density on the cathode due to methanol crossover across the membrane with PDDA-GO bilayer structure is about 1/3 of that with pristine membrane, indicative of a reduction of methanol crossover by 63%. The use of Nafion (R)-PDDA-GO leads to the enhanced power density and improved energy efficiency of the passive DMFC. This study highlights the perspective of the application of GO as methanol-blocking thin film on the surface of Nafion (R) membrane in the DMFC. (C) 2013 Elsevier Ltd. All rights reserved.