Cathodic behavior of BaCoO3 doped with La was investigated in this study for an intermediate temperature solid oxide fuel cell (ITFC). Electrical conductivity of BaCoO3 increased monotonically with an increasing amount of La doped for the Ba site at 1073 K p(O2) = 10(-5) atm. Cathodic overpotential at 1073 K decreased with increasing La content and attained a minimum at X = 0.3-0.5 in Ba1-xLaxCoO3. Since the cathodic overpotential of Ba0.6La0.4CoO3 kept a small value at decreased temperature, Ba0.6La0.4CoO3 is the optimum composition for the cathode of an ITFC among BaCoO3-based oxides. When La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 was used for the electrolyte, the power density of the cell using Ba0.6La0.4CoO3 for the cathode at 1073 K attained a value of 550 mW/cm(2), which is slightly higher than that using Sm0.5Sr0.5CoO3 for the cathode. In addition, a low cathodic overpotential of Ba0.6La0.4CoO3 was also maintained in air. O-18-O-16 exchange reaction was performed to estimate the surface activity for oxygen dissociation. It was found that BaCoO3 exhibits high activity for the oxygen exchange reaction. Therefore, superior cathode property was assigned to the high surface activity of BaCoO3.