X-ray diffraction and microstructures of four as-cast Nb-TiAl alloys were studied. The results indicate that Nb-TiAl alloys of different Nb have different phases. Interrupted oxidation behavior of four as-cast Nb-TiAl alloy at 1000℃ in static air were studied using thermo-gravimetric analysis. The results indicate that moderate Nb can enhance oxidation resistance of the alloy by analyses of Kinetic curves of interrupted oxidation of TiAl based alloy of high Nb content - at 1000℃.