The local structure of electrochemically lithium-inserted SnO-B2O3 glasses was investigated by several spectroscopic techniques to clarify a lithium insertion mechanism into the glasses. 50SnO.50B(2)O(3) (mol %) glass showed two plateaus around 1.5 and 0.5 V (vs. Li+/Li) on the lithium insertion process and exhibited a high capacity of 1240 mAh g(-1) in the case of using a conventional liquid electrolyte. On the first plateau (1.5 V vs. Li+/Li), metallic Sn with small domains was formed and the coordination environment at boron in the glass network was not changed. On the second plateau (0.5 V vs. Li+/ Li), the borate glass network was rearranged by a transformation from tetrahedral BO4 to trianglar BO3 boron units, which provides an additional free space compensating an increase in volume followed by a formation of Li-Sn alloy domains. Hence, the larger the fraction of tetrahedral BO4 unit is in the SnO-B2O3 glasses, the higher the charge-discharge capacities are. The SnO-B2O3 glasses are applicable to all-solid-state lithium rechargeable batteries as anode materials with high capacity. (C) 2003 The Electrochemical Society.