PURPOSE: To obtain a lightweight Mg base alloy excellent in strength and corrosion resistance, good in formability and suitable for the use in aerospace industry by specifying the compsn. composed of Li, Al, rare earth metals, Zn, Mn and Mg.

CONSTITUTION: This Mg alloy has a compsn. substantially contg. 7 to 12% Li, preferably, about 8.5 to 10.5% 2 to 6% Al, 0.1 to 2% rare earth metal, ≤2% Zn and ≤1% Mn, furthermore contg., if necessary, about ≤5% Si, and the balance Mg with accompanying elements and impurities, and in which B, Cd, Hf, Ag and Na are not substantially present. As the rare earth metal, Sc is particularly used. Furthermore, in the componental compsn., preferably, the content of Li+Al is regulated to about 11.5 to 15%, and the total content of impurities is regulated to about <0.1%. The alloy has a hexagonal close-packing and a body-centered cubic structure, and after holding to a high temp. for about ≥one week, it maintains ≥90% room temp. yield strength. The alloy can be formed into an aerospace industry structural member or a composite matrix contg. SiC by forging, extrusion, rolling or the like.