Porous, hierarchical CuO microspheres (MSs) have been successfully synthesized through a facile, surfactant-free carbonate-assisted hydrothermal method. A growth mechanism based on self-aggregation and decomposition of precursor Cu₂(OH)₂CO₃ nanoparticles and Ostwald ripening under hydrothermal conditions is proposed to explain the formation of CuO MSs. Then the CuO MSs are encapsulated with GO through engineering the ionic strength in solution and applied as anode materials for lithium ion batteries, which demonstrates that CuO/GO exhibits significant improvements over the bare CuO MSs. It can deliver a high reversible capacity of 500 mA h g⁻¹ after 500 cycles, with 80% capacity retention of the second reversible capacity (625.8 mA h g⁻¹) at a current density of 0.5C. This is much higher than 233.5 mA h g⁻¹ of the bare CuO MSs at the same rate. Such significantly enhanced electrochemical performance of the CuO/GO hybrid can be attributed to the synergistic effect of successful integration of the CuO MSs with the highly conductive and flexible GO sheets. This study demonstrates that facile structural tuning of the metal oxide in combination with advantageous carbon materials is a promising way to fabricate anodes for high-performance lithium-ion batteries.