Due to the superior capacity for lithium storage, metallic tin and germanium are considered as one of the candidate anodes for the next generation of lithium ion batteries. Herein, metallic tin and germanium particles are successfully prepared by using a mild replacement reaction between metallic sodium and the corresponding tetrachloride under room temperature. The as-obtained metals exhibit nanocrystals of several nanometers. Used as anode of lithium-ion batteries, the as-obtained metallic nanocrystals display improved cycling stability, superior rate performance and high reversible capacity as well. Furthermore, it provides a facile approach to fabricate other electrochemically active metallic nanocrystals by using this mild and environmental benignity replacement reaction.