12-phosphotungstic acids were mixed with hexadecyltrimethylammonium chloride to form self-assembled organic/inorganic nanostructures. The composite materials are thermally stable and exhibited large proton conductivity when the composite was annealed at higher temperatures. High proton conductivity of 0.01 S/cm at 150 degreesC under a saturated humidity condition was obtained for the PWA ammonium salt product, which was formed by annealing the initial nanostructures at 400 degreesC. (C) 2004 Elsevier B.V. All rights reserved.