The oxidative kinetics of U-2 wt%Nb alloy with pearlitic structure at different stages (parabolic stage, transition stage, linear stage and decline stage) was uncovered using the oxygen-consumption and the reflectance spectroscopy method. Compared with U, the diffusive niobium enhances oxidative corrosion resistance of U-2 Nb at initial period. Unlike general cognition, the effect of niobium decreases with oxidative corrosion aggravating after initial period. It may result from mismatch of Nb-rich and Nb-deficient structure. The mechanism proposed in this work is propitious to the design of U-Nb binary alloys to improve their anti-corrosion property.