The main purpose of this work consists on the preparation of single layered zirconium oxynitride, ZrNxOy, thin films, deposited by rf reactive magnetron sputtering. The depositions were carried out by varying the process parameters such as substrate bias voltage and flow rate of the reactive gases. Independently of O content, the samples prepared with oxygen fractions revealed crystalline structures basically constituted by face centred cubic ZrN grains. Atomic force microscopy (AFM) observation showed lower values of surface roughness for low oxygen fractions and a second region where roughness grows significantly, corresponding to the highest oxygen fractions. Ion bombardment promoted a continuous smoothing of the surface up to a bias voltage of -66 V. At a bias voltage of -75 V, roughening is again observed. The small increase of film hardness in low oxygen fractions ZrNxOy. films was attributed to lattice distortions occurring as a result of the possible oxygen incorporation within the ZrN lattice and also grain size reduction. Residual stresses appeared to be an important parameter to explain the observed behaviour, namely in the group of samples prepared with variation in the bias voltage. Regarding colour variations, it was observed a clear dependence of the obtained colorations with oxygen fraction. (C) 2004 Elsevier B.V. All rights reserved.