A new series of magnesium-rare earth master alloys have been developed by the electrowinning method with subsidence cathode in the KCl center dot NaCl-RECl(3) system. The electrolysis conditions were studied. Experimental results showed that the optimum for electrolyte at 850 degrees C and 10 similar to 20wt% RECl(3) content in the molten salt system. The current efficiency of electrolyte increased with increasing the rare earth content and reach the maximum at the content of 20% RECl(3). The current efficiency gradually decreased with increasing cathode current density. The component of master-alloys was analyzed using ICP-MS and chemical method. A series of magnesium-rare earth master-alloy, Mg-Y, Mg-Nd, Mg-Ce, Mg-La, Mg-Nd-rich and Mg-LPC were successfully prepared and the content of rare earth is adjustable between 5-20%.