Zr-Si-N coatings were deposited on steel and silicon substrates by reactive sputtering of a composite Zr-Si target. The coatings were oxidised in air in the 600-750 degreesC temperature range. As-deposited and oxidised films were characterised by X-ray diffraction, micro-Raman spectroscopy, X-ray photoemission spectroscopy and glow discharge optical emission spectroscopy. The oxidation behaviour of Zr-Si-N coatings was compared to that of ZrN ones. It was demonstrated that addition of silicon in the 3-5 at.% range into ZrN-based coatings promotes the onset of oxidation by nearly 100 degreesC. The structure of the oxide layer was strongly dependent on the film's silicon content: monoclinic zirconia for ZrN films, a mixture of monoclinic and tetragonal zirconia for intermediate silicon concentration and tetragonal zirconia for high silicon content. Finally, the stabilisation of the tetragonal form is discussed taking into account the occurrence of doping elements in the oxide layer, the intrinsic stresses in the oxidised films and the mean crystal size of zirconia grains. (C) 2004 Elsevier B.V. All rights reserved.