Thermal oxidation tends to improve surface performance of titanium and its alloys by thickening the native passive oxide layer. In the present work, investigation of thermal oxidation in a wide range of treating temperatures between 500-850°C was carried out for commercially pure titanium (CP-Ti) to determine the optimum thermal oxidation parameters by evaluating the corrosion resistance. Characterization of modified surface layers was made by X-ray diffraction analysis and surface hardness measurements. The results showed that the rutile TiO2 layer was formed on the surface of specimens, and the thickness of the TiO2 layer and the surface hardness increased with the treating temperature. Evaluation of corrosion resistance indicated that the optimum thermal oxidizing temperature was 700°C under air atmosphere.