A two-step reaction mechanism of oxide materials as anodes in rechargeable lithium batteries was found by comparing discharge-charge curves and cyclic voltammograms of eight oxides. It was also proved by experiments of ex-situ XRD of Sb2O3 anode nt discharged state. HRTEM images of nanometre SnO at deep discharged state confirmed the two-step reaction mechanism and showed the typical microstructure character of reaction products: the particle was composed of a large amount of nanosized Li-Sn alloy which dispersed in the Li2O matrix. Furthermore, it was found that the electrochemical properties of SnO anodes were influenced by the particle size of SnO.