We prepared epitaxially grown Cr2O3 thin films on Al2O3 (0001) substrate by using radio frequency magnetron sputtering at room temperature followed by a rapid-thermal annealing process. It is shown that the phase and the crystallinity of as-grown samples depend on the flow ratios of the working gas (Ar/O-2). X-ray diffraction (XRD) results show that oxygen-rich CrO3 phase having preferred orientation is formed when sputter-grown at room temperature under the working gas (Ar/O-2) flow ratios of 9:1 and 7:3. XRD Phi-scanning results exhibit that annealing causes the oxygen-rich CrO3 phase to transform into epitaxial Cr2O3 phase, which is confirmed by X-ray photoemission spectroscopy. The samples grown at the gas flow ratio of 9:1 exhibit very smooth surfaces with root mean square roughness of 0.1-0.3 nm. (C) 2010 Elsevier B.V. All rights reserved.