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°C annealed samples were studied, respectively. The as-synthesized salt was crystal and kept Keggin structure even being annealed at 400°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°C associated with Pt catalyst had excellent assistant catalytic effect on methanol electro-oxidation and displayed a high proton conductivity of 2mScm−1 at 30°C under 96% relative humidity condition.