Α new type of a high temperature liquid metal-air energy storage cell based on solid oxide electrolyte has been successfully demonstrated at 750 °C by feeding metal Sn. In order to understanding the initial size effect of metal as a liquid fuel, we report here the impact of the thermal and electrochemical oxidation behavior of nano Sn (∼100 nm), comparing with micro-sized (∼5 µm) and macro-sized (∼350 µm) Sn. The thermogravimetric analysis and the monitoring OCV test indicate that the distinct property of nano-sized Sn results in a favorable thermal oxidation behavior near the melting point and a promising power performance due to enhanced fuel transport to the anode. However, the accumulated Sn oxide at the reaction interface during a discharge test towards the limitation of further electrochemical oxidation.