The chemically covalent polyethylenimine-siloxane hybrids doped with various amounts of ortho-phosphoric acid (H3PO4) were prepared and characterized by FTIR, DSC, TGA, and solid-state NMR spectra. The protonic conduction behavior of these materials was also investigated by means of impedance measurements. These observations indicate that the hydrogen bonding and protonic interactions exist between the dopant H3PO4 and the hybrid host, resulting in an increase in T-g of polyethylenimine segments. These hybrids are thermally stable up to 200 degrees C from TGA analysis. Conductivity studies show an Arrhenius behavior characteristic and the Grotthus-like proton conduction, and a high conductivity of 10(-2)-10(-3) S cm(-1) at 110 degrees C in dry atmosphere for the hybrid membrane with H3PO4/EI of 0.5. (c) 2006 Wiley Periodicals, Inc.