A disadvantage to the application of Ti3Al is its poor high temperature oxidation resistance. It is found that the element Nb or(and) Si can greatly reduce the oxidation rate of Ti3A1. A hot stage in situ X-ray diffractometer was used to determine the formation sequence of the oxide layers. At 800°C, TiO2 as well as Al2O3 was detected on the surface of binary Ti3Al at the beginning of the oxidation process. The addition of 5 at % Si to Ti3Al alloy did not favor the formation of an A12O3 layer. On the contrary, it inhibited the onset of Al2O3 to nearly 20 hours from the start of the oxidation process at the temperature of 800°C. The Nb addition also did not promote the formation of Al2O3. TiO2 formed first on the surface of Ti3Al-11 at % Nb alloy while TiN and TiAl formed consequently. Al2O3 was further delayed to 20 hours from the beginning of the oxidation process. When the Nb addition increased to 15 at %, however, TiN and TiAl were not found. It is suggested that the favorable effect of Nb and Si to the oxidation resistance of Ti3Al alloy is not due to their promotion of A12O3 layer, but probably due to some other mechanisms, such as the formation of TiN which serves as a diffusion barrier and decreases porosity in the TiO2 layer.