Polarization properties of ceria-based anodes dispersed with nanometer-sized Ru catalysts, which we developed for medium-temperature solid oxide fuel cells, were greatly improved by controlling the composition and microstructure. Among samaria-doped ceria (SDC) anodes with compositions of (CeO2)(1-x)(SmO1.5)(x)(0 less than or equal to x less than or equal to 0.4) a SDC anode with x = 0.2 was found to exhibit the maximum current density at a given overpotential at temperatures of 800 to 1000 degrees C, when operating under a hydrogen atmosphere. This high current density is a direct result of improved conductivities of both oxide ions (sigma(ion)) and electrons (sigma(e)). Attaching a very thin film of SDC onto a yttria-stabilized zirconia electrolyte before coating the Ru-dispersed SDC layer appreciably lowered the anodic overpotential for the SDC. The current densities on the improved Ru-SDC anode at a potential of -0.9 V vs an air reference electrode were 0.8 and 1.4 A/cm(2) at 800 and 900 degrees C, respectively.