A (TiNb)3(SiAl)C2 solid solution was designed and synthesized to improve the high-temperature oxidation resistance of Ti3(SiAl)C2. After doping with Nb, the oxidation resistance of Ti3(SiAl)C2 is improved. Its oxidation kinetics follows parabolic behavior up to 1300°C. The oxide scale formed on (TiNb)3(SiAl)C2 is thinner and smaller in grain size than that on Ti3(SiAl)C2 under the same oxidation condition. The beneficial effect of Nb doping on the oxidation resistance of Ti3(SiAl)C2 mainly results from the decreased concentration of oxygen vacancies and titanium interstitials in the rutile form of TiO2, and the inhibited generation of excessive voids in the oxide scale.