Abstract: The filling metals of Mg58.5Al31.5Sn10 and Mg58.5Al31.5Sn10RE were prepared. The microstructure and properties of the filling metals and the corresponding butt joints of AZ61A magnesium alloy were investigated by analysis methods including SEM, XRD, DSC, wetting and tensile strength test, etc. The results have shown that the microstructures of Mg58.5Al31.5Sn10 filling metal and its joint mainly consist of massive Mg2Sn, binary eutectic phase of Mg17Al12and Mg2Sn, and a small amount of ternary eutectic phase of Mg17Al12, Mg2Sn andα-Mg. However, the microstructures of Mg58.5Al31.5Sn10RE filling metal and its joint chiefly comprise ternary eutectic phase of Mg17Al12, Mg2Sn andα-Mg, binary eutectic phase of Mg17Al12and Mg2Sn, and a small amount of Al-RE phase. Compared with Mg58.5Al31.5Sn10, the microstructure of Mg58.5Al31.5Sn10RE is more homogeneous and finer, solid-liquid phase line temperatures obviously decrease, the melting temperature range shorts 6 ℃, and the spreading area increases by 5.4%. The butt joint average tensile strength of AZ61A magnesium alloy with Mg58.5Al31.5Sn10RE filling metal raises by 8.6% than that of with Mg58.5Al31.5Sn10RE. The butt joints of both filling metals exhibit the brittle fracture morphology.