The ORR activity and durability of Fe-containing non-precious N-doped carbon catalysts was studied in acidic medium using a rotating ring-disk electrode voltammetry and XPS technique. The catalysts (Fe/PI) were synthesised from the pyrolysis of the Fe(acac)3 and polyimide nanoparticle (PI) mixture. The catalytic activity and durability of Fe/PI is superior to the conventional phthalocyanine-based catalyst. The onset potential of ORR was 0.915 V vs. RHE in 0.5 M H2SO4 which is very close to that on a commercially available Pt/C catalyst. The Fe/PI catalyst sustains its activity and stability even after 11,110 repeating potential-steps between 0.6 and 1.0 V vs. RHE in O2-saturated 0.5 M H2SO4 and 1,110 potential cycles between 1.0 and 1.5 V vs. RHE in argon-saturated 0.5 M H2SO4, respectively. The kinetic and mechanistic analyses of the ORR on this catalyst indicate that the ORR, as a whole, follows 4-electron (parallel) pathway. The N 1s XPS spectra before and after the durability test indicate that pyridinic and graphite-like nitrogens take part in improving the ORR activity, whereas nitrogen oxides have the negative role in the ORR. The loss of ORR activity was observed after the acid washing of the catalysts which suggests the role of Fe in the overall 4-electron reduction of O2.