A family of amphiphilic organic/inorganic hybrid electrolyte membranes has been synthesized through sol-gel processing of bridged polysilsesquioxane macromolecules. The membrane doped with acidic moieties such as 12-phosphotungstic acid (PWA), shows proton conductivities larger than 10(-2) S/cm at temperatures up to 160 degreesC. An effect of the nanostructure of the amphiphilic hybrid macromolecules on proton conductivity is discussed. The proton conducting properties of the bridged alkylene hybrid membranes with various organic bridging groups were investigated in the range of 100 to 160 degreesC and at a relative humidity from 20 to 100%. The octane hybrid membrane showed a conductivity of approximately 3 x 10(-2) S/cm up to 160 degreesC and a temperature stability up to 400 degreesC. A stable conductivity above 100 degreesC, which is relatively insensitive to the humidity level, suggests a robust conductive channel structure in the flexible macromolecules. The organic/inorganic hybrids synthesized from amphiphilic polysilsesquioxane families show promise for applications in intermediate temperature polymer electrolyte fuel cells. (C) 2003 The Electrochemical Society.