PURPOSE: To produce a heat resistant Mg alloy in which fine intermetallic compounds having low specific gravity and a high m.p. are uniformly dispersed by successively executing an LDC process and plastic working to the stock having the compsn. of an Mg alloy contg. a specified amt. of alloy elements AE such as Si.

CONSTITUTION: The stock having the compsn. of an Mg alloy contg. at least one kind of alloy element AE selected from Si, Ge and Sb by 1.3≤AE≤20wt.% is subjected to an LDC process to produce a porous intermediate body. Then, this porous intermediate body is subjected to plastic working to produce the heat resistat Mg alloy. In this way, the heat resistant Mg alloy in which fine intermetallic compounds having low specific gravity and a high m.p. are uniformly dispersed and capable of easily satisfying the heat resistant strength to be required can be obtd.