The electrical properties of yttria stabilized zirconia (YSZ) electrolyte containing different amounts of CuO (0-1 mol%) have been studied. The complex impedance diagrams showed an increase in the grain boundary resistivity with CuO addition. The bulk resistivities were comparable to those of the CuO free YSZ except for the sample containing 1 mol% CuO which showed a small increase in resistivity. The results showed the possibility to sinter YSZ at low temperature 1250 degrees C to a very high sintered density by adding a small amount of CuO (0.3 mol%). The conductivity of the latter is nearly equal to that of YSZ sintered at 1500 degrees C. This might be a step forward in the development of oxygen pumps by reducing the electrolyte sintering temperature which leads to better quality and low cost. (c) 2007 Published by Elsevier B.V.