W, have prepared novel proton conducting inorganic-organic hybrid membranes from 3-aminopropyltriethoxysilane (APTES) and H2SO4 by the sol-gel method. The resulting poly(3-aminopropylsitsesquioxane sulfate or hydrogensulfate) (PAPS-SO4/-HSO4) membranes were thermally stable up to 300 degrees C. From the results of IR spectra, it was confirmed that sulfuric acids in the membranes react with amino groups of PAPS to form ion complexes. XRD patterns of the PAPS-SO4/-HSO4 membranes showed diffraction peaks assigned to hexagonal structure, which is probably formed by stacking of rodlike polysiloxanes with the ion complexes extruded outside. The PAPS-SO4/-HSO4 membranes with a molar ratio of H2SO4/APTES = 1.0 showed high proton conductivities of 2 x 10(-3) S cm(-1) at 200 degrees C under dry condition. (c) 2007 Elsevier B.V All rights reserved.