MnO powder materials are investigated as anode active materials for Li-ion batteries. Lithium is stored reversibly in MnO through conversion reaction and interfacial charging mechanism, according to the results of ex situ XRD, TEM and galvanostatic intermittent titration technique. A layer of the solid electrolyte interphase with a thickness of 20–60nm is covered on MnO particles after full insertion. MnO powder materials show reversible capacity of 650mAhg−1 with average charging voltage of 1.2V. It can deliver 400mAhg−1 at a rate of 400mAg−1. The cyclic performance of MnO is improved significantly after decreasing particle size and coating with a layer of carbon. Among observed transition metal oxides, MnO shows relatively lower voltage hysteresis (<0.7V) between the discharging and the charging curves at 0.05C. In addition to its environmental benign feature and high density (5.43gcm−3), MnO seems a promising high capacity anode material for Li-ion batteries among transition metal oxides. However, the initial columbic efficiency is less than 65% and the voltage hysteresis is still too high. The origins of them are discussed.