Nanocrystalline Si-mesocarbon microbeads (MCMB) composite anode materials were prepared by ballmilling. Scanning electron microscopic observation showed that the spherical shape of MCMB particles can be retained via moderate ballmilling. Ballmilling conditions have an impact on the capacity and cyclability of nanocrystalline Si-MCMB composites. The optimized Si-MCMB composite anode demonstrated a reversible capacity of 1066 mAh/g with good cyclability. A reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the Si-MCMB electrode. (C) 2004 The Electrochemical Society.