To reduce the polarization at oxygen electrode of a rechargeable lithium oxygen battery, Ba0.9Co0.7Fe0.2Nb0.1O3-delta (BCFN9721) perovskite oxide was prepared and applied as a bi-functional electro-catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Lithium oxygen battery with an oxygen electrode composed of 80% Ketjen Black (KB) and 20% BCFN9721 delivered a discharge voltage plateau of 2.63 V, which is the highest among different composition ratios of KB and BCFN9721 in the oxygen electrodes. Adding 20% BCFN9721 into KB could effectively reduce the polarization and achieve better bi-functional activities for the electrochemical reactions at positive electrode, especially for the OER. The lithium oxygen battery using BCFN9721 perovskite oxide as the electro-catalyst could run stably for 24 discharge/charge cycles with a fixed capacity of 1000 mAh g(electrode)(-1). The charge polarization could be significantly reduced by BCFN9721 catalyst, thus alleviating the formation of undesired discharge products caused by the corrosion of carbon and decomposition of the electrolyte. Ba0.9Co0.7Fe0.2Nb0.1O3-delta perovskite oxide can be a promising bi-functional electro-catalyst for the oxygen electrode of rechargeable lithium oxygen batteries. (C) 2016 Elsevier Ltd. All rights reserved.