Two types of nanosize intermetallic alloy powders, NiSi and FeSi, are prepared by high-energy ball-milling. The alloys are used as electrode materials in lithium test cells. During lithium insertion into the alloy electrodes, Si acts as active centres, which react with Li to form Li x Si alloys. A high lithium storage capacity of 1180 mA h g−1 is observed for the NiSi electrode, with some reversibility. A mechanism for the reaction of NiSi and FeSi with Li+ is proposed.