Purpose: The main aim of the research was the investigation of the structure and adhesion of AlTiCrN, CrAlSiN and TiAlSiN coatings deposited by physical vapour deposition technology on the X40CrMoV5-1 hot work tool steel and the X6CrNiMoTi17-12-2 austenitic stainless steel substrate. Design/methodology/approach: Observations of surface and microstructure of the deposited coatings were carried out on cross sections in the SUPRA 35 scanning electron microscope. The microhardness tests of coatings were made with the SHIMADZU DUH 202 ultra-microhardness tester. The cohesion and adhesion properties of the coatings were made using the scratch test on the CSEM REVETEST device. Findings: It was found that the coatings present a compact structure, without any visible delaminations or defects. The morphology of the fracture of coatings is characterized by a dense structure, in some cases there is a columnar structure. The coatings demonstrated good adhesion to the substrate. The critical load L C2 lies within the range of 39-47 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa). Practical implications: The process of covering steels with the thin PVD coatings is currently the most commonly method used to extend their life. Investigations of those coatings determining their scratch-resistant properties and structure enable to pick out the optimum coatings for given industrial applications. Originality/value: The results of the investigation provide useful information on microstructure and scratch-resistant properties of the quaternary coatings deposited on the hot work tool steels and austenitic stainless steels. Reference to this paper should be given in the following way: K. Lukaszkowicz, A. Kriz, J. Sondor, Structure and adhesion of thin coatings deposited by PVD technology on the X6CrNiMoTi17-12-2 and X40CrMoV5-1 steel substrates, Archives of Materials Science and Engineering 51/1 (2011) 40-47.