The preparation and characterization of two new families of lithium-conducting solid-state electrolytes is reported. Both systems are silica (SiO2) - polyethyleneglycol (PEG(n)) hybrid materials with (type I) or without (type II) covalent organic-inorganic chemical bonds. Their electrical conductivity has been studied by complex impedance spectroscopy between 20 degrees C and 100 degrees C in the frequency range 1 Hz to 10 MHz as a function of the polymer chain length (200 < n < 1900), polymer concentration and lithium concentration (4 < [O]/[Li] < 80) The highest room-temperature ionic conductivity (sigma congruent to 6 x 10(-2) S cm(-1)) has been found for type II material for ratios [O]/[Li] = 15 and PEG(300)/TEOS = 1.0. The effect of the chain length on the polymer mobility has been studied by nuclear magnetic resonance by measuring the Li+ line widths and the spin-lattice relaxation time T-1 between -100 degrees C and + 100 degrees C. The bonded chain mobility increases with the chain length ( type II) while the opposite occurs with unbonded chain material (type I). Both types of materials present high ionic conductivity at room temperature and are adequate as Li+-conducting electrolyte in all solid-state electrochemical devices.