Novel single ion-conductive inorganic/organic composites were prepared from 95(0.6Li(2)S.0.4SiS(2)).5Li(4)SiO(4) oxysulfide glass and a high molecular weight branched poly(oxyethylene) (POE). The ionic conductivity of the composites increased with an increase of the glass. The ionic conductivity of the composite with 1 wt.% branched poly(oxyethylene) was in the orders of 10(-5) S/cm at 30 degreesC and 10(-4) S/cm at 80 degreesC. The composite exhibited an electrochemical stability window up to ca. 4.5 V versus Li+/Li and thermal stability against lithium metal up to 200 degreesC. Addition of LiClO4 to the polymer matrix of the composite improved the ionic conductivity. In this case, the composite was a dual-ion conductor, i.e., both Li+ and ClO4- contributed to the conductivity.