We develop platinum-iron-nickel (PtFeNi) trimetallic alloy catalysts having a chemically ordered L1(0)-type superlattice structure. The PtFeNi catalyst annealed at 800 degrees C possesses a superlattice structure and exhibits oxygen reduction reaction (ORR) activity that is much higher than that of the disordered PtFeNi catalysts and a commercial Pt catalyst supported on carbon black. Moreover, the ORR specific activities in the PtFeNi trimetallic systems are enhanced more than those in the PtFe and PtNi bimetallic systems. Analyses of in situ X-ray absorption spectroscopy reveals Pt-Pt bond distances in the PtFeNi annealed at 800 degrees C (2.70-2.72 angstrom) are shorter than those in a commercial Pt (2.77 angstrom), leading to a suitable balance of oxygen species chemisorption energies on the Pt atoms. In addition, high durability of the PtFeNi catalyst with a superlattice structure is demonstrated. Therefore, tuning the atomic structures of Pt-alloy catalysts by the formation of a superlattice structure and trimetallic system effectively enhances both ORR activity and durability.