A process of modification of natural graphite materials as anode for lithium ion batteries was attempted. The process started with the treatment of natural graphite with concentrated hydrochloric acid and concentrated sulfuric acid in a thermal autoclave, followed by the in situ polymerization of resorcinol-formaldehyde resin to coat the graphite, then heat-treatment. SEM, XRD, Raman and electrochemical charge-discharge analysis showed that the surface defects and impurities on natural graphite were eliminated by purification of the concentrated acids, and carbon-film encapsulation modified the surface structure of the graphite and reduced its BET surface area. The as-obtained natural graphite sample presented an initial charge-discharge coulombic efficiency of 88.4% and a reversible capacity of 355.8 mAh g(-1). The proposed process paves a way to prepare a promising anode material with excellent performance with low cost of natural graphite for rechargeable lithium ion batteries. (C) 2007 Elsevier Ltd. All rights reserved.