The electron and hole conductivity of [(ZrO2)(1-x)(CeO2)(x)](0.8)(YO1.5)(0.2) (x = 0-1, 0.1 step) solid solutions was measured by dc polarization method using a modified Hebb-Wagner's ion blocking cell at 973, 1073, 1173, and 1273 K as a function of oxygen partial pressure. All measured data were fitted to the sum of the electron conductivity having a p(O2)(-1/4) dependence and the hole conductivity having a p(O2)(1/4) dependence. At all temperatures, with increasing CeO2 concentration, the electron conductivity drastically increased at x = 0-0.4 and slightly decreased at x = 0.6-1.0, leading to a maximum at x = 0.4-0.5. The logarithmic hole conductivity linearly increased with CeO2 concentration for x = 0-1. (c) 2006 The Electrochemical Society.