CeO2-based electrolytes are promising candidates for intermediate temperature SOFC applications. However, they are prone to electronic conduction at low partial pressures of oxygen. This paper describes the effect of yttria stabilized zirconia (YSZ) additions on (CeO2)(0.8)(GdO1.5)(0.2) materials between 0 and 20 mol% YSZ [8 mol% YSZ (8YSZ) and 3 mol% YSZ (3YSZ)], on the ionic conductivity. For all samples examined, a single cubic-phase was observed, stable between room temperature and 800 degrees C. Between 1 and 5 mol% 8YSZ and 3YSZ, the ionic conductivity was very similar to (CeO2)(0.8)(GdO1.5)(0.2) with no YSZ additions. However, the ionic domain increased from P-O2 = 10(-15) to 10(-17) atm, showing greater stability of the system containing YSZ.