3D NiO microspheres assembled from porous nanosheets are prepared and evaluated as an anode material for lithium-ion batteries, showing excellent electrochemical performance with high lithium storage capacity, and satisfactory cyclability and rate performance. The NiO microspheres deliver a first discharge capacity of 1242 mA h g⁻¹ with a reversible capacity up to 820 mA h g⁻¹ after 100 cycles at a current of 100 mA g⁻¹ in a half cell, also exhibiting an ameliorative rate capacity of 634 mA h g⁻¹ at the current of 1 A g⁻¹. The high lithium storage performance can be mainly ascribed to the porous nanosheets, which improve lithium ion transfer, provide sufficient electrode/electrolyte contact areas, and more efficiently accommodate the volume change that occurs with the lithiation/delithiation process. Moreover, the 3D microsphere architecture is also helpful for enhancing the electrochemical performance of the lithium-ion battery. The results indicate the great potential of the 3D NiO microspheres assembled from porous nanosheets for use as an anode material for lithium-ion batteries.