The interfacial reactions were found in Al2O3/Cr2O3 layers prepared by ion assisted deposition of a-Al2O3 coatings by anodic evaporation in the arc discharge on Cr2O3/stainless steel substrate. The X-ray photoelectron spectra (XPS) measurements (core levels and valence bands) revealed the diffusion of Cr-ions from substrate, which is accompanied by partial substitution of Al-sites. This conclusion is confirmed by specially performed density functional theory calculation in the coherent potential approximation of Al1.95Cr0.05O3, which in full agreement with XPS valence band data shows the location of Cr-impurity states in the region of the energy gap of pure Al2O3 and Fermi level crosses the Cr 3d-band of the effective cationic atom.