Fe-N/C nanofiber (Fe-N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO3)(3)) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH = 13) and 0.5 M H2SO4 (pH = 0) electrolyte solutions. Higher treatment temperature and NH3 atmosphere were preferred by the Fe-N/CNF catalysts, and especially the concentration of Fe(NO3)(3) solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe-N/CNFs prepared using 0.5 wt% Fe(NO3)(3) solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H2SO4 solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe-N/CNF catalysts.