Appropriate conditions for depositing hard Cr₂O₃ coatings by reactive sputtering techniques have yet to be defined. To fill this gap, the effect of principal deposition parameters, including deposition pressure, temperature, Cr-target voltage, and Ar/O₂ ratio, on both the structure and mechanical properties of chromium oxide coatings was investigated. A relationship between processing, structure, and the mechanical properties of chromium oxide coatings was established. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the morphology, structure, and chemical compositions of the coatings that were prepared. An optical profilometer was employed to measure both the roughness and thickness of the coatings. The hardness and Young’s modulus of the coatings both as-deposited and after annealing conditions were measured by nanoindentation. The results showed that depositing hard Cr₂O₃ coatings is a highly critical task, requiring special deposition conditions. Cr₂O₃ coatings with a high hardness of approximately 25 GPa could be achieved at room temperature, at a low pressure of 1.6 × 10⁻¹ Pa, where Cr-target voltage and oxygen content were 260 V and between 15–25 vol % of total gas, respectively. A dense stoichiometric Cr₂O₃ structure was found to be responsible for the high chromium oxide coating hardness observed.