The large over-potential during the battery operation is a great obstacle for the application of Li-O-2 batteries. The porous structure and electrical conductivity of the electrocatalysts are significant for the electrocatalytic performance of Li-O-2 batteries. In this work, a porous Co3O4/GN nanocomposite (Co3O4 nanorods anchored on graphene nanosheets) is prepared via a facile hydrothermal method assisted with heat treatment. The unique structure of Co3O4/GN endows efficient electrocatalystic activity for Li-O-2 batteries. In comparison to the Co3O4, the Co3O4/GN demonstrates a better cycle performance showing more than 40 cycles with a 1500 mAh g(-1) capacity limit strategy at a current density of 300 mA g(-1), and a reduced over-potential of 110 mV at high current density (1200 mA g(-1)). The Co3O4/GN also displays a high initial specific capacity (7600 mAh g(-1)) and a good reversibility in full cycle with a coulombic efficiency of 99.8% in the first cycle. The impressed cyclability, specific capacity, rate performance, and low over-potentials indicate that the as-prepared Co3O4/GN nanocomposite is a promising catalyst candidate for reversible Li-O-2 batteries. (C) 2018 Elsevier B.V. All rights reserved.