Rechargeable magnesium batteries have attracted considerable attention because of their potential high energy density and low cost. However, their development has been severely hindered because of the lack of appropriate cathode materials. Here we report a rechargeable magnesium/iodine battery, in which the soluble iodine reacts with Mg to form a soluble intermediate and then an insoluble final product magnesium iodide. The liquid-solid two-phase reaction pathway circumvents solid-state Mg diffusion and ensures a large interfacial reaction area, leading to fast reaction kinetics and high reaction reversibility. As a result, the rechargeable magnesium/iodine battery shows a better rate capability (180 mAh g at 0.5 C and 140 mAh g at 1 C) and a higher energy density (∼400 Wh kg ) than all other reported rechargeable magnesium batteries using intercalation cathodes. This study demonstrates that the liquid-solid two-phase reaction mechanism is promising in addressing the kinetic limitation of rechargeable magnesium batteries.