For the preparation of solid polymer electrolytes with high conductivity and good mechanical properties, organically modified ceramic electrolytes were prepared based on low molecular weight poly(ethylene glycol), lithium salt and an inorganic matrix produced by sol-gel process of tetraethoxysilane and a new poly(ethylene glycol)-modified sol-gel precursor which was synthesized by the reaction of monomethoxy terminated poly(ethylene glycol) and 3-isocyanatopropyl triethoxysilane. Transparent and self-supporting films were obtained showing high ionic conductivities (3.2 x 10(-6) similar to 1.4 x 10(-4) S/cm) at room temperature.