Insights into high temperature oxidation of Al 2 O 3 -forming Ti 3 AlC 2 are made to understand the sub-parabolic oxidation rate and the absence of Al-depletion zone beneath the protective Al 2 O 3 scale. The scale results from selective oxidation of Al that migrated from Ti 3 AlC 2 according to Ti 3 AlC 2 +3/2y O 2 →Ti 3 Al 1−y C 2 +1/2y Al 2 O 3 , leaving Al vacancy in the substrate. Inward diffusion of oxygen via grain boundaries of the Al 2 O 3 scale predominates for the scale growth. The Al 2 O 3 grains grow with time, yielding sub-parabolic oxidation kinetics. The Al diffuses in a fast manner, accounting for the absence of Al-depletion zone.