A first-principles study was conducted to investigate the effect of several types of Pt- and N-doped carbon nanotubes (CNTs), with varying doping concentrations, on the oxygen reduction reaction (ORR) at the air cathode in lithium-air batteries and fuel cells. The computational results reveal that Pt-doped CNTs exhibit a greater O-O bond elongation, permitting an easier cleaving of O-O conjugations, than that of Pt-adsorbed CNTs. In addition, the search for a Pt substitute is conducted and this paper intends to study the feasibility of N-doped CNTs. Our results show that the catalytic activity of Pt-doped CNTs is higher than that of N-doped CNTs as revealed from the cleaved bond length of O-O. However, N-doped CNTs outperform both pristine and Pt-doped CNTs on the specific thermal capacity which can yield a higher structural stability in the ORR operation. The simulation results show that the energy gaps are shorter with higher concentrations of Pt or N doping. After comparing the slope tendencies between the Pt and N-doped cases, N-doped CNTs exhibit a more dramatic decline than that of the Pt-doped CNTs. That will theoretically result in an easier catalytic activity for the ORR process. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.064205jes]