In order to realize large-scale Mg-Zn-Y alloys with high strength and high heat resistance, we have developed a unique casting process to produce a large homogeneous ingot investigating the mechanical properties of the extruded alloys. First homogeneous ingots (335 mm x 850 mm) were prepared by a unique stir casting process. Then large-scale extruded alloys (100 mm) were prepared at 648 K with the extrusion ratio of 10. The Mg-Zn-Y alloys have exhibited higher yield and fatigue strengths than those of aluminum alloys. The yield strengths of the aluminum alloys have decreased drastically above 473 K, whereas those of the Mg-Zn-Y alloys have not. It is noteworthy that the yield strength (200 MPa) and the fatigue strength (75 MPa) of the Mg-Zn-Y alloys at 523 K are about twice and 1.2-1.4 times as high as those of the aluminum alloys respectively. Moreover, the creep strengths have been equivalent or higher than those of aluminum alloys. From the above results, we have verified that even being made by the large-scale extrusion, the Mg-Zn-Y alloys possess higher strength than those of heat resistant aluminum alloys.