The Mg-MM and Mg-Nd master alloys were prepared through the ingot metallurgy method under the protection of a special flux. The thermodynamic behaviors of different rare earth elements in the molten Mg alloys were investigated.Two experimental alloys, Mg-3.0 wt pct MM-0.7 wt pct Zn-0.7 wt pct Zr and Mg-2.8 wt pct Nd-0.7 wt pct Zn0.7 wt pct Zr, were prepared. The hardness and tensile properties of experimental alloys were measured and the microstructures were observed. The results showed that the rare earth elements could react greatly with the Mg chloride in the flux. The Mg-Nd-Zn-Zr alloy displayed a good aging hardening effect. The dispersed metastable phase β (Mg3Nd) is an important strengthening phase to improve the tensile properties of this alloy. So the Mg-Nd-Zn-Zr alloy has better tensile properties and elongation than those of the Mg-MM-Zn-Zr alloy, and the ductile fracture character could be observed. The microvoid coalescence is the dominant fracture mechanism in this alloy.