Acceptor-doped ceria can be used as an oxygen-permeating membrane due to its high mixed ionic and electronic conductivity at high temperature in low oxygen partial pressure. However, the mechanical weakness prevented its use at a high temperature in the reducing condition. In this study, alumina was added to strengthen the ceria without severely reducing the electrical conductivity. The electrical conductivity of alumina-added ceria, (Ce0.8Gd0.2O2-delta)(1-x)+(Al2O3) (x=0, 0.019, 0.0475, and 0.095: hereafter, GDC20, GDCA2, GDCA5, GDCA10, respectively), was measured as a function of temperature (1300 degrees C-1600 degrees C) and oxygen partial pressure (Po-2: 1-10(-13) atm). As the alumina content increased, the ionic conductivity decreased due to the formation of a secondary phase (similar to Gd0.8Ce0.2AlO3) which caused a decrease in the Gd content in the ceria. The conductivities of GDC20 with and without alumina addition showed maxima in the conductivity curves in the reducing condition when plotted versus log Po-2. The oxygen-permeation values of GDC20, GDCA5, and GDCA10, measured at 1500 and 1600 degrees C in the high Po-2 range (0.21-0.02 atm), were much higher than that of doped-zirconia. The permeation rate slightly decreased with the alumina addition. The oxygen permeation of the ceria-based sample, GDCA10, in the low Po-2 range (2x10(-10)-2x10(-8) atm) was successfully measured at 1600 degrees C for the first time and showed much higher (>50 times) oxygen permeability than that of the doped-zirconia. (C) 2007 Elsevier B.V. All rights reserved.