Ionic conduction in both stoichiometric and nonstoichiometric perovskite-type oxide sinters BaxCe0.90Y0.10O3-alpha (x = 0.80-1.20) has been investigated over temperature range 600-1000 degrees C. X-ray powder diffraction patterns of the specimens sintered at 1650 degrees C for 10 h suggested that these oxides consist of a single phase of orthorhombic perovskite-type BaCeO3, except for Ba0.80Ce0.90Y0.10O3-alpha that was observed to contain both perovskite and CeO2 phases. These oxides exhibited excellent protonic conduction under hydrogen-containing atmosphere, whereas they showed poor oxide ionic conduction with predominant electronic one under oxygen-containing atmosphere at high temperatures. Among these oxides, Ba0.95Ce0.90Y0.10O3-alpha showed the highest conductivities under dry air, wet air and wet hydrogen.