Abstract: Low yield strength and poor heat resistance are two major obstacles to the application promotion of magnesium alloys. In this study, heat-resistant high silicon Mg-9Al-3Si magnesium alloy with excellent high temperature performances is prepared by combining rapid solidification and hot extrusion processes, and its microstructure and mechanical properties are investigated. Results show that the grains of the rapidly solidified Mg-9Al-3Si ingot are refined, and that the distribution of the fine Mg₂Si phase is greatly improved. The rapidly solidified Mg-9Al-3Si extruded magnesium alloy also exhibits a weak texture with a maximum textural strength of only 4.61 in the (0001) basal plane. The tensile strength, yield strength and elongation of the rapidly solidified Mg-9Al-3Si extruded magnesium alloy are 403.0 MPa, 353.0 MPa and 12% at room temperature, 203.0 MPa, 199.0 MPa and 27% at 150 ℃, and 119.0 MPa, 110.0 MPa and 30% at 200 ℃. The high-temperature strengths, especially the yield strength at 150 ℃, are excellent.