Novel proton-conducting membranes comprising polymer/inorganic materials based on linear polyethyleneimine (LPEI)/SiO2 nanocomposites synthesized through sol-gel processing have been prepared. 3-Glycidyloxypropyl-trimethoxysilane (GLYMO) has been used to cross-link the LPEI to afford improved heat resistance. The addition of trifluoromethanesulfonimide (HTFSI) during membrane processing doped the amine groups of LPEI to form immobilized Bronsted acid-base pairs, which provide the hybrid membrane's proton conductivity. The resulting membranes show a proton conductivity as high as 1 x 10(-2) S/cm at 90 degrees C, 100% relative humidity and 5.6 x 10(-5) S/cm at high temperatures (>= 130 degrees) under anhydrous conditions. The effects of temperature, humidity and mobility of active groups on the conductivity are discussed. (C) 2008 Elsevier B.V. All rights reserved.