Heteropoly acid entraped in nano silica matrix was prepared by the microemulsions method. The primary particle size was less than 400nm and it decreased with the content of the heteropoly acid. When these silica particles were blended with sulfonated polyethersulfone, the HPA could be effectively immobilized in aqueous environment. The conductivity of this composite electrolyte was 1.4x10(-3) S/cm with the 15% HPA.