The oxygen permeability, J(o2), in CeO2 doped MSZ, [(ZrO2)(1-x)(CeO2](0.9)(MgO)(0.1) (x = 0.1 similar to 0.6), was measured at 1100-1750 K under the oxygen partial pressures, P-o2, of 0.2-1 x 10(-4) atm. The specimens were predominantly oxide-ion conductors with n-type electronic conduction. The oxygen permeabilities normalized by temperature, T, and P-o2, log Jr = log [J(o2)/(T(P-o2(II-1/4)-P-o2(I-1/4))], were proportional to 1/T and increased with temperature. At 1100-1500 K, Jr increased exponentially for x less than or equal to 0.4 and the electronic activation energy, E, was about 2 eV and was independent of x. At 1500-1750 K, Jr increased exponentially for x less than or equal to 0.4, while for x > 0.4 it showed a saturation tendency and the E values were 1.86 +/- 0.10 (x = 0.1), 1.67 +/- 0.08 (x = 0.2), 1.50 +/- 0.16 (x = 0.3), 1.39 +/- 0.05 (x = 0.4), 1.22 +/- 0.06 (x = 0.5) and 1.32 +/- 0.04 (x = 0.6) eV. The log Jr of x = 0.6 was a little higher than that of x = 0.5 at 1100-1280 K (E = 2.10 +/- 0.07 for x = 0.5 and 1.79 +/- 0.06 for x = 0.6 eV), while at 1280-1750 K, the value of x = 0.6 was a little lower than that of x = 0.5 (E = 1.57 +/- 0.06 for x = 0.5 and 1.49 +/- 0.03 for x = 0.6 eV at 1280-1500 K).