Phosphotungstic acid (H3PW12O40, HPW) molecules were anchored onto carbon nanotubes (CNTs) by electrostatic self-assembly using poly(diallyldimethylammonium chloride) (PDDA); subsequent incorporation of these particles into poly(vinyl alcohol) (PVA) afforded a methanol-blocking membrane for direct methanol fuel cell (DMFC) application. The prepared membrane exhibited a significantly higher proton conductivity of 9.4mScm−1 at 60°C and satisfactory proton conductivity stability over a 120-h test than a PVA membrane. Moreover, the composite membrane showed a decrease in the methanol permeability by ∼40% compared to a PVA membrane (6.10×10−7cm2s−1) and much better proton-to-methanol selectivity because of a higher dimensional stability after the incorporation of CNTs. A single DMFC based on the prepared membrane exhibited a maximum power density of 16mWcm−2 at 60°C. Thus, CNT-PDDA-HPW/PVA membranes have a great potential as an alternative proton exchange membrane for DMFC application.