Abstract: he oxidation of uranium metal was studied by X-ray diffraction(XRD) and Rietveld method in the range of 25-150 ℃ and at 300 ℃, respectively. The processes of oxidation to UO₂ and U₃O₈ were analyzed by XRD in order to observe the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO₂ in the temperature range of 25-150 ℃ was initially nonlinear, but switched to linear at long reaction time, that is, there exist two stages in the UO₂ growth kinetics: nonlinear portion and linear portion. Using the kinetic data of linear portion the activation energy of oxidation is obtained to be about 46.0 kJ/mol. The U₃O₈ forms gradually on UO₂ layer at 300 ℃, which accords with the nucleation-and-growth kinetics mechanism.