Alumina was added to doped ceria and its effect on the grain conductivity was studied. The electrical conductivities of Gd, Sm, or Y-doped ceria (CeO2) with or without alumina addition were measured as a function of temperature (250-700 degrees C) in air. Impedance measurement enabled the separation of the grain conductivity and the grain boundary conductivity. With alumina addition of 1, 2, and 5 mol%, the grain conductivity of alumina-added samples below 400 degrees C increased with the accompanied grain size increase and the migration enthalpy decrease. A model was proposed to explain the observation that includes the low-conductivity region in the grain of doped ceria. (C) 2008 Elsevier B.V. All rights reserved.