The ability to tailor the size and composition of metal particles at the nanoscale could lead to improved or new catalytic properties. This paper reports the results of an investigation of the preparation and the characterization of platinum-nickel-iron (PtNiFe) ternary alloy nanoparticles. The synthesis of monolayer-capped ternary PtNiFe nanoparticles involved controlling the ratios of metal precursors, capping agents, and reducing agents in a single organic phase. The average diameters of the resulting nanocrystalline cores were well controlled between 1.4 and 1.8 nm with high monodispersity (±0.2-0.4 nm). The catalysts were prepared by loading the as-synthesized PtNiFe nanoparticles onto a high surface area carbon support and subsequent thermal treatment optimized for achieving effective shell removal and alloy formation, as well as controllable size, composition and metal loading. The catalysts were characterized using TEM, DCP-AES, FTIR, TGA, and XRD techniques. The catalysts were also examined for their intrinsic kinetic activities for the electrochemical oxygen reduction reaction. It is shown that the ternary catalysts are highly active towards molecular oxygen electrocatalytic reduction. Implications of our findings for the exploration of the new nanostructured catalyst materials for applications in fuel cell catalysis are also discussed.