To improve the La1-xSrxMnO3-delta-yttria- stabilized zirconia (LSM-YSZ) cathode performance of intermediate temperature solid oxide fuel cells (SOFCs), Sm0.6Sr0.4CoO3-delta (SSC) perovskite nanoparticles are incorporated into the cathodes by a reaction-infiltration process. The SSC particles are similar to 20 to 80 nm in diameter, and intimately adhere to the pore walls of the preformed LSM-YSZ cathodes. The SSC particles dramatically enhance single-cell performance with a 97% H-2 + 3% H2O fuel, between 600 and 800 degrees C. Consideration of a simplified triple-phase boundary reaction geometry indicates that the enhancement may be attributed to the high electrocatalytic activity of SSC for electrochemical reduction of oxygen in a region that can be located a small distance away from the strict triple-phase boundaries. The implication of this work for developing high-performance electrodes is also discussed. (C) 2006 The Electrochemical Society.