Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.