The oxidation behavior of a full-lamellar Ti-42.5Al-8Nb-0.2W-0.2B-0.1Y alloys with different colony sizes was investigated by using thermogravimetric method at 900℃ for 100 hours in air. The microstructure and composition of the alloy as well as the oxide scales were analyzed by OM, SEM, EDS and XRD. It was found that the oxidation kinetic of the present TiAl alloys accorded with the parabolic law, and the alloy with larger lamellar colony have a better oxidation resistance than that of the one with smaller lamellar colony. The weight gain after 100 h oxidation was 7.62 g/m₂ and 6.45 g/cm₂, respectively for these two alloys, and correspondingly the thickness of oxide scale was about 7μm and 5μm, respectively. Base on the analysis of oxidation kinetic and microstructure characterization, we concluded that lamellar colony size has a significant effect on the oxidation behavior of TiAl alloys.