The microstructure and aging precipitated phases of Mg-12Gd-2Y-1Sm-0.5Zr alloy have been studied by micro-analysis XRD and EDS. Through the analysis it is found that the precipitated phases in the alloy contains Mg24Y5, Mg5Gd and Mg41Sm5. The tensile strength peak of Mg-12Gd-2Y-1Sm-0.5Zr alloy appears at 250 .