Electrode reaction was compared between single crystal YSZ and yttria doped ceria coated YSZ with a platinum point electrode in H-2-H2O atmosphere at 1173 K. The thickness of the ceria layer was altered between 200 and 1000 nm. The ceria coating on the YSZ surface gave no effect on the electrode interfacial conductivity from AC impedance measurements. The electrode interfacial conductivity was either proportional to 1/4 or 1/2 powers of P(H-2), while it was independent of P(H2O) both at the YSZ and the ceria coated YSZ. There was little difference in the DC polarization curves between YSZ and ceria-200 nm coated YSZ, except that of the ceria-1000 nm coated YSZ. Hence, the surface catalytic activity does not affect the rate of the electrode reaction. The present results do not confirm the effect of high electronic and ionic conductivity of ceria.