Electrochemical behavior of a new class of glass-polymer composites (GPC), consisting of (100-x) vol% (0.56Li(2)S . 0.19B(2)S(3) . 0.25LiI) glass and x vol% (P(EO)(6) . LiN(CF3SO2)(2)) polymer with x = 7, 13 and 25, has been investigated in cells with different electrodes. Results show that the addition of the polymer to the glass powder increases not only the mechanical flexibility but also the ionic conductivity. The combination of impedance spectroscopy and 4-probe dc measurements indicates that the GPC with x = 13 vol% polymer exhibits the highest lithium ion conductivity, varying from 3 x 10(-4) Ohm(-1) cm(-1) at room temperature to 1.4 x 10(-3) Ohm(-1) cm(-1) at 80 degrees C. In addition, the GPC electrolytes with x = 13 vol% seem to be relatively stable against Li, LixMn2O4, and carbon electrodes, since interfacial impedances between the electrolyte and the electrode materials are relatively constant at 70 degrees C for up to 375 hours.