Abstract: A process for producing a protective film on a magnesium based metallic substrate comprising producing successive deposits by vapor phase chemical deposition of at least one intermediate layer of metallic aluminum, and at least one surface layer of metallic oxide, and for the intermediate aluminum layer using a precursor chosen of triisobutylaluminum, heating the substrate to a temperature between 250.degree. C. and 320.degree. C., and for the surface layer selecting an appropriate precursor, heating the substrate to an appropriate temperature and introducing the precursor vapor to produce a protective film having a high surface hardness and strong adherence to the magnesium based substrate with high inertness in the electrochemical series, and forming an effective protection under both static and dynamic conditions.