Perovskite-type complex oxide La0.5Ba0.5CoO3-δ, promising cathode material for solid oxide fuel cells and precursor for synthesis of double perovskite LaBaCo2O6-δ, was prepared as a single-phase material. Its oxygen content was measured by two independent techniques in the temperature range 1000-1100 °C and at oxygen partial pressures corresponding to the stability field of cubic phase. The defect chemistry of this material was studied using the measured δ = f(pO2, T) dependences. The defect structure model based on the localized nature of the electronic defects was proposed and successfully verified.