The detailed density functional theory calculations were performed to screen the oxygen reduction reaction (ORR) catalytic activity of several kinds of Fe-Sx/C catalysts such as Fe-S-2/C, Fe-S(2)x(2)/C, Fe-S-3/C, Fe-S-4/C, and Fe-S-6/C. The results suggest that only the Fe-S-2/C structure could maintain its initial planar structure after the geometry optimization, indicating that it is most likely to have ORR catalytic ability. Further investigations find that the O-2 molecule is firstly chemisorbed on the Fe-S-2 active site with a stable side-on mode, and then is gradually reduced to H2O following a 4e(-) OOH dissociation pathway. Both thermodynamic adsorption energies of ORR intermediates and kinetic activation energies of proton transfers indicate that the current Fe-S-2/C catalytic site possesses the comparable catalytic activity to that of precious Pt catalysts. Furthermore, compared with Pt(111) surface, it also has very excellent tolerance to some impurities such as sulfur compounds (SO2, H2S), carbon compounds (CO), and nitrogen compounds (NO, NH3). (C) 2018 The Electrochemical Society.