The temperature and the oxygen partial pressure dependencies of the hole and electron conductivities of 20 mol %-REO1.5 doped CeO2 (RE = Yb, Y, Gd, Sm, Nd, La) were measured by the dc polarization method using a Hebb-Wagner's ion blocking cell at 973-1273 K in the oxygen partial pressure range of log{p(O-2)/(MPa)} = -9 to -1. All measured data were fitted to the sum of the electron conductivity having a p(O-2)(-1/4) dependence and the hole conductivity having a p(O-2)(1/4) dependence. Among the six RE-doped ceria, the neodymium-doped ceria had the highest hole conductivity, and the lanthanum-doped ceria had the highest electron conductivity, although essentially no dopant dependence was observed in both contributions. The apparent activation energies of electron conduction were almost twice larger than those of hole conduction. Essentially no dopant dependence was observed in the activation energy. Using the activation energy, 2.05 eV, for concentration change in Ce0.8Y0.2O1.9 derived from recent literature values for oxygen nonstoichiometry, the activation energy, 0.2 eV, for the electron mobility was evaluated. (C) 2004 The Electrochemical Society.