Proton conductive inorganic-organic hybrid membranes were synthesized from 3-glycidyloxypropyltrimethoxysiane (GPTMS), phenyltriethoxysilane (PhTES) and hydroxyalkylphosphonic acid. Two kinds of hydroxyalkylphosphonic acids, 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) and hydroxyethanephosphonic acid (HEPA), were incorporated into the membranes as functional molecules for proton conduction. FF-IR and Raman studies revealed the presence of phosphonic acid groups in the hybrid membranes. C-13 and Si-29 NMR confirmed that a three-dimensional siloxane network was formed in the prepared hybrid membrane by hydrolysis and condensation reactions. DTA-TG analysis showed that these membranes were thermally stable up to 200 degrees C. The HEDPA-based system was found to have higher proton conductivities than the HEPA-based one. The proton conductivities of the hybrid membranes increased with the phosphonic acid content and temperature up to 130 degrees C. The conductivities ;of the HEDPA/GPT/MS/PhTES membranes = 1/1.6/0.4 were 1.0 x 10(-1) and 4.5 X 10(-4) S cm(-1) at 100% relative humidity and non-humidified conditions, respectively, at 130 degrees C. (C) 2008 Elsevier B.V. All rights reserved.