Transition metal oxides and carbonates are emerging anode materials for lithium-ion batteries based on conversion reactions. In this paper, MnO sphere is simply prepared by decomposition of the spherical MnCO3 precursor, and multi-walled carbon nanotubes (MWNTs) are employed to modify their lithium storage capabilities. It is found that the MnO system has superior battery performance over MnCO3 although both of their performances could be significantly improved by carbon nanotube backbones. In particular, the MWNTs/MnO composite sphere shows an outstanding electrochemical performance with a comparatively lower lithium extraction potential. The reversible specific capacity at 35 mA g−1 is ∼1005 mA h g−1 with an initial coulombic efficiency of ∼68%. After 200 cycles at 130 mA g−1, the capacity is slowly decreased from ∼722 mA h g−1 to ∼597 mA h g−1 indicating a retention of ∼83%. Under a high current rate of 715 mA g−1 (∼1.6 C), it could still deliver ∼447 mA h g−1. The high conductivity of MWNTs, unique spherical morphology of the composite, facile electron and Li+ transportations in the electrode/electrolyte interface, self-accommodation of the large volume change during discharge/charge and synergetic lithium storage from each component are ascribed for the advanced performance.