Effects of the mischmetal addition in range of 0.4% to 1.7% on the microstructure and mechanical properties of die casting magnesium AZ91D were investigated to improve the elevated temperature mechanical properties of the alloy.The results reveal that mechanical properties of die casting magnesium alloy AZ91D-0.4%MM at 100℃ is near to those of die casting magnesium alloy AZ91D at room temperature.The ultimate tensile strength, 0.2% yield strength and elongation of die casting magnesium alloy AZ91D at 170℃ were 178 MPa, 129 MPa and 20%, respectively.In comparison, the ultimate tensile strength, 0.2% yield strength and elongation of die casting magnesium alloy AZ91D-0.4% at 170℃ reached to 206 MPa, 142 MPa and 26%, respectively increased by 15.7%, 10% and 30%.Proper addition of mischmetal can enhance the mechanical properties at elevated temperature, which is attributed to the formation of Al-RE phases with high thermal stability.Hence sliding of grain boundaries and cracks can be effectively hindered by Al-RE phases.