Abstract: The air electrodes with different mass ratio of active carbon to carbon nanotube as catalyst layer material have been prepared. The electrocatalytic performances for oxygen reduction were evaluated by means of polarization curve and electrochemical impedance spectroscopy(EIS). The results disclosed that carbon nanotube content in the catalyst layer obviously affected the electrocatalytic activity. The air electrode with the mass ratio of active carbon to carbon nanotube of 50:50 showed the highest electrocatalytic activity, i.e., the output current density reached 300~500 mA/cm² when the overpotential was 400~600 mV. The EIS of the as-prepared air electrode consisted of two semi-circles, in which the high frequency zone was ascribed to the ohmic process and the low frequency zone to the electrochemical kinetic process. The addition of carbon nanotube in the catalyst layer decreased greatly ohmic and kinetic impedance and thereby produced greater enhancement in performances. The mass transport process in the electrode was dominated by the thin film diffusion. The low catalytic activity of the air electrode prepared by the pure carbon nanotube appeared to be a consequence of the penetration of electrolyte into the porous structure. The equivalent circuit of the air electrode was proposed and the simulated kinetics data was analyzed.