The development of a promising bifunctional electrocatalyst for oxygen catalytic reactions such as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable owing to the sluggish kinetics that limit these reactions. In this study, CoFe2O4 nanoparticles anchored on nitrogen and sulfur co-doped mesoporous carbon spheres (CFO/NS-MCS) were prepared as nonprecious metal catalysts, using a facile pyrolysis and hydrothermal treatment process. The co-doping of N and S into the carbon spheres was achieved using thiourea, which played a key role in the bimetallic covalent coupling in the NS-MCS. The as-prepared CFO/NS-MCS exhibited a more promising ORR catalytic performance compared with that of commercial Pt/C, which was attributed to the presence of highly active sites. Remarkably, the CFO/NS-MCS catalysts also showed a high OER catalytic performance comparable with that of commercial RuO2/C in the aspects of onset potential and Tafel slope, and showed a better durability for oxygen catalytic reactions in an alkaline solution. The approach indicated in this research can be applied to develop high-performance electrocatalysts for practical implementation in energy storage and conversion devices. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.