This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl-KCl-MgCl2-AlCl3 melts at 943 K to form Mg-Li-Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg-Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg-Al leads to the formation of a liquid Mg-Li-Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than -0.47 A cm(-2) in LiCl-KCl-MgCl2 (0.525 mol kg(-1)) melts containing 0.075 mol kg(-1) AlCl3. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is -2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than -2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that alpha, alpha + beta and beta Mg-Li-Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.