The development of low-cost catalysts for the oxygen reduction reaction is an important step for the commercialization of proton-exchange membrane fuel cells. Pd is a robust catalytic material for this reaction and is considered as an alternative to Pt due to its similarity with Pt. However, since Pd is oxidized at a lower positive potential than Pt, it is less active and less stable than Pt in an oxygen reduction reaction. We developed a simple synthesis route for N-doped carbon-caged Pd catalysts supported on carbon nanofibers using Pd-polyaniline composites. Oxidative polymerization of aniline spontaneously produced Pd-polyaniline composites with the reduction of Pd ions. The subsequent heat treatment of Pd-polyaniline composites produced N-doped carbon-caged Pd catalysts, in which the polyaniline served as the source of the N-doped carbon cage. The catalytic activity and stability of the synthesized catalyst were dependent on the heat-treatment temperature and the synthesis method. The optimized catalyst heat-treated at 500 °C (Pd@NC/CNF500 (NDA, US)), which was synthesized with nondistilled aniline under ultrasound irradiation, exhibited higher catalytic activity and stability in oxygen reduction reaction than general Pd catalysts reported in literature. Pd@NC/CNF500 (NDA, US) showed high performance even in the unit cell test.