Deposits elaborated by PVD processes are of great importance in mechanical industry,which requires high performance tools with always increasing lifetime. Outstanding physical and chemical properties have been recently obtained with a new generation of coatings, characterized by the coexistence of two nanometric phases. Such phase distribution is achieved either by successive deposition of nanolayers of different nature (named multilayer or 2D material) or by dispersing crystalline nanodomains into an amorphous matrix (named nanocomposite or 3D material). Deposited onto tool steels, these coatings can be a solution to sustain high stresses encountered in severe machining because, in such conditions, coated parts have not only to fulfil high tribologic properties, but also to be thermally resistant. This paper presents some data concerning the oxidation behaviour of coated pieces in relation to the coating nanostructure. Nanocomposite magnetron sputtered TiBN, as well as arc evaporated multilayered TiN/CrN deposits are investigated in comparison with microstructured TiAlN, TiN or CrN layers. Nature of oxides developed during 24 hours at 700degreesC in air is determined by XRD and observed by SEM, while protective potentialities (oxidation critical temperature and kinetic parameters) are deduced from thermogravimetric analysis. Whatever the configuration, 2D or 3D, a beneficial influence of the nanostructure is observed on the corrosion resistance at high temperature. Corrosion rates are particularly decreased for CrN base coatings, whereas TiN coating leads to a thick cracked rutile layer, damaging from an oxidation point of view. Oxidation protection due to multilayered CrN/TiN deposit is significant, which is explained by the fact that, the formed Cr2O3 layer is a barrier against the progression of the oxide layer.