Powder X-ray diffraction (XRD) analysis showed that the single phase perovskite-type structure of Ba1-xLaxCe0.90-xY0.10+xO3-alpha (0 less than or equal to x less than or equal to 0.40, alpha = 0.05) could be maintained in a wide region of doping level by simultaneous partial substitution of La3+ for Ba2+-site and Y3+ for Ce4+-site in BaCeO3. The conduction properties of these oxides were investigated using various electrochemical methods in the same concentration of oxygen vacancy (cu = 0.05). At high oxygen partial pressure, these oxides exhibited a mixed oxide ionic and p-type electronic conduction while at low oxygen partial pressure their conduction was almost protonic. Among these oxides, BaCe0.90Y0.10O3-alpha exhibited the highest conductivities with a value of 1.24 X 10(-1) S/cm in dry oxygen, and 5.65 X 10(-2) S/cm in wet hydrogen at 1000 degrees C. Both of the proton and oxide ion conductivities under oxygen and under hydrogen atmospheres decreased monotonically with the increasing substitution for Ba2+- and Ce4+-sites. The decreases in ion conductivities appear to relate to the decreased free volume (V-f) of crystal lattice as well as the increased distortion of lattice from ideal cubic perovskite structure.