Octahedral PtNi nanoparticles show high activity for the oxygen reduction reaction (ORR) due to the electronic modification effect between the surface Pt atoms and subsurface Ni atoms. However, these electrocatalysts easily degraded and lost their activity because the leaching of Ni from nanoparticles in acid media, which leads to the elimination of electronic modification effect. Therefore, highly active and durable electrocatalysts are needed for the commercialization of ORR catalysts. Herein, we developed the selective halide treated PtNi nanoparticles on Ni atom rather than Pt. This halide adsoprtion blocked the surface Ni sites, prevented the leaching of Ni from nanoparticles, and maintaing the octahedral shape after the stability test. Especially, Br-treated PtNi can effectively prevent the leaching of Ni. Stability test of 10,000 cycles in the 0.6 V to 1.1 V vs. RHE showed that the decrease of mass activity by 52.6% for the as-prepared octahedral PtNi, whereas the decrease of mass activity by 15.0% for the Br-treated octahedral PtNi. The selective halide treatment on Ni sites improved the stability of the highly active octahedral PtNi nanoparticles for the ORR.