Abstract: In this paper, the oxidation of U-2.5%Nb alloy in air at a temperature range of 60-300 ℃ was studied by measuring oxide thickness and weight gain. In addition, the morphologies were examined by using SEM. The results indicate that, under experimental condition, the oxidation of U-2.5%Nb alloy follows a parabolic law in the temperature range of 60-80 ℃, at the temperatures between 100 ℃ and 150 ℃, a paralinear law is presented, however, between 200 ℃ and 300 ℃, the oxidation obeys a linear law. At the parabolic oxidation stage, the activation energy is calculated to be 74.70 kJ/mol, and at the linear oxidation stage， which is 31.48 kJ/mol. The SEM examination reveals that, during the stage of parabolic oxidation, the “surface relief” is produced due to the difference in oxidation rate of alpha phase and gammatwo phase, but the scale is dense and compact. However, when the oxidation changes to the linear-oxidation stage, the scale becomes loose, and the vertical cracks are observed in the scale.