Ionic conduction and Ba2+:Ce4+ site nonstoichiometry in perovskite-type oxide sinters of non-doped BaxCeO3-alpha (0.90 less than or equal to x less than or equal to 1.10) have been investigated. X-ray powder diffraction patterns of these sinters indicated that the specimens with 0.95 less than or equal to x less than or equal to 1.10 were a single phase of orthorhombic perovskite-type BaCeO3,, while the sinter with x = 0.90 was a mixed phase of perovskite and CeO2, impurity. The conduction properties of the specimens with 0.95 less than or equal to x less than or equal to 1.05 were studied electrochemically in the temperature range of 600-1000. The conduction properties of the specimens were strongly influenced by Ba2+:Ce4+ site nonstoichiometry. The specimens with excess Ba showed a predominant ionic conduction (H+ + O2-) With ion transport number larger than 0.5 under hydrogen atmosphere, whereas they showed a poor oxide-ionic conduction (oxide-ion transport numbers < 0.1) under oxidizing atmosphere. Protonic conduction in these specimens under reducing atmosphere could be confirmed by means of electrochemical hydrogen permeation. In contrast, the specimens with x less than or equal to 1.00 showed a predominant oxygen-ionic conduction (oxygen-ion transport numbers >0.8) in oxidative atmosphere, while a poor ionic conduction (ion transport numbers <0.1) was observed in hydrogen.