ZnO was studied as dopant or additive for CeO2 in the concentration range x = 0.00 to x = 0.95 referred to (CeO2)(1-x)(ZnO)(x). From XRD, the solubility limit of ZnO in the bulk of CeO2 estimated as 3 +/- 0.7 mol% at room temperature. The total conductivity was measured for all compositions in air by impedance spectroscopy. The contributions from bulk and grain boundaries were evaluated separately. Additionally, the electronic conductivities were measured using a Hebb-Wagner technique with microelectrodes. Up to the solubility limit, the total conductivity of the bulk in air increases almost linearly with the ZnO content from 300 degrees C to 800 degrees C, the same holds for the p-type electronic conductivity (in the range 600 degrees C-800 degrees C). Hence, zinc ions act as acceptors on cerium sites, zinc doped ceria is a moderate mixed conductor. In the two-phase domain from 3 mol% up to 20 mol%, the total conductivity increases slightly and the partial electronic conductivity dependence remains nearly constant. Starting at 30 mol% ZnO, the grain boundary conduction rises steeply and the electronic conductivity predominates the total conductivity for this and higher ZnO contents reaching 0.03 S/cm at 800 degrees C in air for a sample with the composition x = 0.95 mol%. (C) 2013 The Electrochemical Society. All rights reserved.