Cobalt and nitrogen co-doped reduced graphene oxide (Co-N-rGO) composites are prepared by a facile low-temperature hydrothermal method. Structure characterization reveals that cobalt and nitrogen are co-ordinately attached to the rGO sheets with the formation of covalent C-N and Co-O-C linkages. Cyclic voltammetry and linear sweep voltammetry show that the Co-N-rGO composite possesses higher electrocatalytic activity and four-electron selectivity for oxygen reduction reaction (ORR) as compared to the rGO, Co-rGO and N-rGO. In addition, the Co-N-rGO composite presents excellent stability and durability in alkaline medium comparable to commercial Pt/C. The edge plane CoN2/C, CoN4/C, and basal plane macrocyclic CoN4/C species within the Co-N-rGO structure are proposed to be the active sites performing catalysis in the ORR. The strong covalent linkages between the cobalt/nitrogen and rGO not only enable potent synergy of cobalt, nitrogen and rGO in catalysis, but also ensure structure stability of the composite. Due to the superior ORR activity of Co-N-rGO, high-temperature heat treatment is not able to improve its activity any more. The low-temperature hydrothermal method is anticipated to be used as a low-cost and facile preparation approach for ORR catalysts, and the superb ORR performance of Co-N-rGO endow it with great application potential in fuel cells, metal-air batteries and other ORR-related electrochemical industries. (C) 2018 Elsevier Ltd. All rights reserved.