Proton exchange membrane fuel cells (PEMFCs) are considered as a promising renewable power source. However, the massive commercial application of PEMFCs has been greatly hindered by their high expense and less-satisfied performance mainly due to the sluggish oxygen reduction reaction (ORR) kinetics even on state-of-the-art Pt catalyst. Octahedral PtNi nanoparticles (oct-PtNi NPs) with excellent ORR activity in a half-cell have been widely studied, while their performance in membrane electrode assembly (MEA) has much less reported. Herein, we investigated the MEA performance using the carbon supported oct-PtNi NPs (oct-PtNi/C) as the cathode catalyst. Under the mild acid washing condition, the surface Ni atoms of oct-PtNi/C were largely removed, and the performance of the MEA using the acid-leaching oct-PtNi/C (PNC-A) as the cathode catalyst was greatly improved. The maximum power density of the MEA reached 1.0 W·cm^–2 with the cathode Pt loading of 0.2 mg·cm^–2, which is 15% higher than that using Pt/C as the catalyst. After 30k cycles in the accelerated degradation test (ADT), the MEA using PNC-A as the catalyst showed a performance retention of 82%, higher than that of Pt/C (74%). The results reported here verify the possibility of using PNC-A as an advanced cathode catalyst in PEMFCs, thus enhancing the performance of PEMFCs while lowering the amount of expensive Pt.