To reveal the effects of Al addition on the oxidation mechanisms of 16Cr ODS steel, high temperature oxidation at 1000 ��C of 16Cr and 16Cr-3Al ODS steels with the same Cr content were investigated. After oxidation, the weight gain of the 16Cr ODS steel was relatively higher than that of the 16Cr-3Al ODS steel. The 16Cr ODS steel had triple oxide layers of an outer FeCr2O4 layer, an intermediate Cr2O3 layer, and an inner SiO2 layer, while the 16Cr-3Al ODS steel had double oxide layers of an outer (Cr, Al)2O3 layer and an inner Al2O3 layer. The oxidation mechanisms of both ODS steels were explored through thermodynamic calculations, and the significant improvement in oxidation resistance of the 16Cr-3Al ODS steel compared to 16Cr ODS steel was attributed to the lower diffusion rate of O in Al2O3 than in Cr2O3. The existence form of oxide particles in the oxide layers was illustrated. These findings offer new strategies for enhancement in oxidation resistance of structural materials used in high temperature environment.