We demonstrate how a highly active non-precious metal-based catalyst for oxygen reduction reactions (ORRs) can be prepared using commercially available polyaniline (PANI) as both nitrogen source and carbon precursor. To do this, PANI-derived catalysts are prepared by pyrolyzing PANI and Fe-impregnated PANI (Fe-PANI) in either N-2 or NH3 atmospheres. When the catalyst precursor is pyrolyzed under an NH3 stream, the resultant catalysts (PANI-A and Fe-PANI-A; A denotes treatment with ammonia) have higher microporosities and pyridinic nitrogen contents than those of N-2-pyrolyzed catalysts (PANI-N and Fe-PANI-N; N denotes treatment with nitrogen). Microporosity produced by pyrolysis and pyridinic nitrogen contents are important factors for ORR activity, which is borne out by the better ORR performance of NH3-pyrolyzed catalysts compared to N-2-pyrolyzed samples. In addition, Fe species coordinated with nitrogen serve as a highly active site to facilitate ORR, leading to Fe-PANI-A delivering the best ORR performance among the PANI-derived catalysts. The onset and half-wave potentials of Fe-PANI-A for ORR were measured as 0.916 and 0.787 mV, respectively, better than for commercial Pd/C. Although some degradation in ORR activity of Fe-PANI-A is observed after a durability test, the loss in the half-wave potential is only 52 mV, indicating a relatively stable ORR activity for Fe-PANI-A. It was demonstrated that how non-precious electrocatalysts for oxygen reduction reaction (ORR) could be prepared using a commercial polyaniline (PANI) as a carbon and nitrogen source. NH3-pyrolysis and Fe-impregnation was revealed to be essential to enhance ORR performance of PANI-derived catalyst. The best-performed PANI-derived catalyst showed higher ORR performance than that of a commercial Pd/C.