<p>TiAl-based alloys represent a class of lightweight materials for high-temperature structural applications, offering attractive properties such as low density coupled with high specific strength and excellent strength retention at elevated temperatures. Nevertheless, their resistance to oxidation under high-temperature conditions remains a limitation. This work systematically examines the influence of varying Nb concentrations on both the microstructural evolution and the oxidation behavior of TiAl alloys. The Ti-45Al-xNb (x = 5, 7, 9) alloys were fabricated via vacuum hot-press sintering furnace using refined Ti, Al, and Nb powders. The experimental results show that the TiAl alloys are composed of equiaxed fine-grained <i>γ</i>-TiAl phases and <i>α</i>₂-Ti₃Al phases, and the content of <i>α</i>₂-Ti₃Al phases increases with the increase in Nb content. After oxidation for 100&#xa0;h, the unit-area weight gain of Ti-45Al-xNb (x = 5, 7, 9) alloys was 2.305&#xa0;mg·cm⁻², 2.016&#xa0;mg·cm⁻², and 1.957&#xa0;mg·cm⁻², respectively. Higher Nb content effectively suppresses oxide layer growth, leading to improved oxidation resistance. The oxide layer comprises four distinct regions: TiO₂-, Al₂O₃-, (Ti, Nb) O-, and an Nb-rich inner layer. Nb enrichment in the transition region reduces, thereby enhancing the alloy’ antioxidant properties. As the Nb concentration is elevated from 5 to 9%, the resulting oxide scale exhibits a considerable thinning, with its measured thickness declining from about 10.3&#xa0;μm to 7.7&#xa0;μm. These findings provide a foundation for the development of high-performance TiAl alloys with enhanced oxidation resistance, facilitating broader applications in aerospace and high-temperature valve systems.</p>