Abstract: TiAl alloy with high Nb content, nominally Ti–45Al–10Nb, was prepared by powder metallurgy, and the oxidation resistance at 850, 900, and 950°C was investigated. The high-temperature oxidation-resistance mechanism and oxidation dynamics were discussed following the oxide skin morphology and microstructural evolution analysis. The oxide skin structures were similar for 850 and 900°C, with TiO₂+Al₂O₃ mixture covering TiO₂ with dispersed Nb₂O₅. At 950°C, the oxide skin was divided into four sublayers, from the outside to the parent metal: loose TiO₂+Al₂O₃, dense Al₂O₃, dense TiO₂+Nb₂O₅, and TiO₂ matrix with dispersed Nb₂O₅. The Nb layer suppressed the outward diffusion of Ti atoms, hindering the growth of TiO₂, and simultaneously promote the formation of a continuous Al₂O₃ protective layer, providing the alloy with long-term high-temperature oxidation resistance.