TiAl-based alloys with Nb/Mo were obtained by the cold crucible induction levitation melting method. The oxidation behavior in air at 900 oC for long time was investigated. The phase composition, microstructure and the interface of the oxidation film and the matrix were investigated by means of XRD and SEM equipped with EDS. Combined with the oxidation kinetic analysis, the synergistic effect of Nb and Mo on the oxidation behavior of TiAl-based alloys was explored. With the addition of Nb and Mo, the continuous compact oxidation film decreases the oxidating rate and the mass gain which makes the alloy preserve better oxidation properties compared with that of Ti-46Al-6Nb. Due to the synergistic effect of Nb and Mo, the indiffusion of oxygen atoms can be prevented and the oxidation properties of TiAl-based alloys can be improved.