Proton-conducting composite material was synthesized from 1-butyl-3-methyl-imidazolium chloride (BMImCl) and 12-phosphotungstic acid (PWA). The structure, assistant catalytic effect and ionic conductivity of the composites for the as-synthesized, 200 and 400 degrees C annealed samples were studied, respectively. The as-synthesized salt was crystal and kept Keggin structure even being annealed at 400 degrees C, but the organic part was partly decomposed with increasing of the annealing temperature. The partly decomposed BMIm/PWA salt formed by annealing at 400 degrees C associated with Pt catalyst had excellent assistant catalytic effect on methanol electro-oxidation and displayed a high proton conductivity of 2 mS cm(-1) at 30 degrees C under 96% relative humidity condition. (c) 2005 Elsevier B.V. All rights reserved.