The polarization behaviors of porous samaria-doped ceria anodes coupled with zirconia electrolytes with various ionic conductivities (sigma(ion)) were investigated. The exchange current density, j(0), on such mixed-conducting SDC anodes was not influenced by the sigma(ion) at 900 and 1000 degrees C, whereas j(0) increased proportionally to sigma(ion) at a lower temperature of 800 degrees C. However, the dispersion of nanometer-sized ruthenium catalysts on SDC particles resulted in an increase of j, with increase in a in the entire temperature range between 800 and 1000 degrees C. The observations are well explained kinetically, i.e., the anode performance is controlled by the rate of O2- supply to the anode layer via the electrolyte, as the anodic reaction rate becomes sufficiently high due to highly dispersed Ru electrocatalysts. Consequently it is clear that the use of high-performance electrodes in combination with the solid electrolyte having high al,, is a prerequisite to achieving high performance of solid oxide fuel cells.