The synthesis and characterizations of novel organic-inorganic composite membrane materials formed by poly(2, 5-benzimidazole)/OctaAmmonium POSS® (ABPBI/OA-POSS) are reported. An uniform dispersion of nanoparticles in the membrane with excellent mechanical properties was obtained from ABPBI containing 3% OA-POSS membranes (ABPBI/3OA). Upon impregnation with phosphoric acid, the composite membranes presented higher phosphoric acid uptakes and proton conductivities than that of the pristine ABPBI membranes. The highest proton conductivity of 0.25S/cm was achieved from ABPBI/3OA membrane with 241% of phosphoric acid uptake at 160d̀C without humidification. These properties make them very good candidates as the membranes for polymer electrolyte membrane fuel cells (PEMFCs) at temperatures up to 160d̀C
