This communication describes the preparation of carbon-supported truncated-octahedral Pt3Ni nanoparticle catalysts for the oxygen reduction reaction. Besides the composition, size, and shape controls, this work develops a new butylamine-based surface treatment approach for removing the long-alkane-chain capping agents used in the solution-phase synthesis. These Pt3Ni catalysts can have an area-specific activity as high as 850 mu A/cm(Pt)(2) at 0.9 V, which is similar to 4 times better than the commercial Pt/C catalyst (similar to 0.2 mA/cm(Pt)(2) at 0.9 V). The mass activity reached 0.53 A/mg(pt) at 0.9 V, which is close to a factor of 4 increase in mass activity, the threshold value that allows fuel-cell power trains to become cost-competitive with their internal-combustion counterparts. Our results also show that the mass activities of these carbon-supported Pt3Ni nanoparticle catalysts strongly depend on the (111) surface fraction, which validates the results of studies based on Pt3Ni extended-single-crystal surfaces, suggesting that further development of catalysts with still higher mass activities is highly plausible.