The development of efficient, stable and cost-effective electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), have become one of the most important bottlenecks in pursuing emerging renewable energy storage and environment friendliness technologies. In this study, we have successfully developed encapsulated CuXCo3-XO4 spinel nanocrystals in carbon nanotubes as high-performance bifunctional oxygen electrocatalyst by one-step hydrothermal reaction. As compared with other Co-based materials, the resulting CuXCo3-XO4@C composite presents excellent catalytic performance and outstanding stability for both OER and ORR with ultralow overpotential (eta = 0.358 V) at a current density of 10 mA/cm(2) and half-wave potential (E-1/2 = 0.82 V) in alkaline solution, respectively. The developed strategy to encapsulate spinel into carbon nanomaterials via a controllable pathway, may open new opportunities for the encapsulation structures of other catalysts. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.