To find a clue for the design of high-performance electrodes for solid oxide fuel cells (SOFCs), the polarization properties of Pt electrodes attached to zirconia electrolytes with various ionic conductivities were investigated at 800- 1000 degrees C. The IR-free anodic polarization in hydrogen was greatly affected by the ionic conductivity of the electrolyte, and it obeyed the Tafel equation. The exchange current density increased in proportion to the square of the ionic conductivity for all electrolytes operated at 800-1000 degrees C, while the transfer coefficient (n alpha(a) = 2) was independent of the temperature and of the conductivity of electrolytes. According to our analysis, the rate-determining step is not a simple electron transfer from oxide ions but a recombination step involving discharged oxygen atoms adsorbed on the Pt electrode/electrolyte interface; an increase in the rate of transport of oxide ions to the interface, for example, by using an electrolyte with higher-ionic conductivity, reduces the anodic overpotential greatly.