This paper addresses the structural, mechanical and tribological properties of chromium oxide thin films produced by post-annealing of Cr thin films. First, chromium thin films were deposited on Si substrate by DC magnetron sputtering technique, and then post-annealed at different temperatures (200-600 degrees C) with flow of oxygen. Crystallographic structure of samples was obtained using X-ray diffraction (XRD) method. The XRD patterns showed Cr3O structure for annealed samples at 200 degrees C and 300 degrees C and Cr2O3 structure for annealed samples at 500 degrees C and 600 degrees C. The sample annealed at 400 degrees C also showed a transition (mixed) phase consisting of both of these phases. Nano-strain investigation for all samples showed compressive strain. Surface physical morphology of samples was studied by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). These studies showed smaller grains and smoother surfaces for annealed films at lower temperatures, while the increasing of annealing temperature caused the increasing of grain diameter and surface roughness. Nano-indentation and scratch tests were used to investigate the mechanical and tribological properties, respectively. The results showed that the post-annealing of Cr thin films was not a suitable method for preparation of Cr2O3 hard coatings; however this method was suitable for production of Cr3O phase with higher hardness and lower scratch volume and friction coefficient values. (C) 2013 Elsevier B. V. All rights reserved.