Seawater-activated battery has received tremendous attention due to the increasing demand for underwater devices. Mg alloy is one of the promising candidates for seawater-activated battery anodes due to the favorable electrochemical characteristics, such as a relatively negative electrode potential (?2.37 V vs. standard hydrogen electrode (SHE)), high theoretical specific capacity (2 189 mAh/g), and low density (1.74 g/cm3). However, the Mg-based anodes always exhibit severe self-discharge in the aqueous electrolyte and the generated products adhered to the anode strongly impede the active dissolution of anode materials. The intent of this work is to study the effect of indium addition and subsequent heat treatment on the electrochemical properties of magnesium anode, thus develop a novel magnesium anode material.