As a main impurity in primary lithium metal, magnesium is difficult to remove because of the very close relative volatility of the two metals. Electrochemical refining provides a possibility to completely remove Mg in the LiCl-KCl melt prior to Li reduction. MgCl 2 reduction processes in LiCl-KCl-MgCl 2 melt were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry and chronopotentiometry. Then potentiostatic electrolysis was carried out and Mg ( ) ion was reduced onto a liquid lead cathode from the LiCl-KCl-MgCl 2 melt at the Mg deposition potential. The results show that Mg ( ) is reduced in one step with two-electron transfer. The reduction potential of Mg ( ) was well defined. The reduction of Mg( ) results in Li ( ) underpotential deposition at 0.2V more negative potential than that of Mg( ) reduction. Therefore, in order to prevent Li ( ) from codeposition with Mg, accurately controlling Mg ( ) reduction potential during the potentiostatic electrolysis was necessary. Ninety three to 99 % removal rate of MgCl 2 was achieved after 8-12 h electrolysis when liquid lead was used as cathode.