TeO_x thin films were deposited at various O₂/Ar gas-flow ratios by a reactive RFmagneton sputtering technique from TeO₂ and Te targets. X-ray diffraction (XRD) results revealed that the TeO_x thin films were amorphous. The structure and chemical composition of the TeO_x thin films were investigated by fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The optical characteristics of the TeO_x thin films were investigated by an Ellipsometer and a UV-VIS-NIR spectrophotometer. According to the O₂/Ar gas-flow ratios, the atomic composition ratio of TeO_x thin films was divided into two regions(x=1-2, 2-3). Different optical characteristics were shown in each region. With an increasing O₂/Ar gas-flow ratio, the refractive index of the TeO_x thin films decreased and the optical bandgap of the films increased.