Electrical conductivity of mixed calcia/yttria-stabilized zirconia (CYZ) was measured by the complex impedance method in the temperature range from 600 to 1 100 K and compared with those of yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia, respectively. Non-linear Arrhenius behavior was observed for all the three samples examined. It was shown that in both high- and low-temperature ranges, the introduction of CaO as the third component into the system ZrO2-Y2O3 would result in increases in both the activation energy for conduction, E, and the pre-exponential factor, sigma(0). Using the experimentally determined values of E and sigma(0), it was predicted that the conductivity of CYZ would be higher than that of YSZ when temperature increases above 1350 K. This phenomenon can be attributed to the fact that CYZ has a larger sigma(0) value mainly due to its higher oxygen vacancies concentration compared with YSZ. (C) 2002 Elsevier Science B.V. All rights reserved.