Platinum nanoparticles (Pt NPs) on carbon black (CB) have been used as catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells for a while. However, this catalyst has suffered from aggregation and dissolution of Pt NPs as well as CB dissolution. In this study, we resolve those issues by developing perfluorosulfonic acid (PFSA)-functionalized Pt/graphene as a high-performance ORR catalyst. The noncovalently bonded PFSA remarkably decreases the dissolution and aggregation of Pt NPs. Moreover, unlike typical NP functionalization with other capping agents, PFSA is a proton conductor and thus efficiently develops a triple-phase boundary. These advantageous features are reflected in the improved cell performance in electrochemical active surface area, catalytic activity, and long-term durability, compared to those of the commercial Pt/C catalysts and graphene-based catalysts with no such treatment.