The long-term isothermal oxidation behavior of bulk Ti2AlC in air and 100% water vapor has been investigated in the 1000-1300 degrees C temperature range. The kinetics, for oxidation up to 120 hours, follows a cubic rate law in both environments -air and water vapor. The kinetics was found to be slightly faster for hydrothermal oxidation compared to oxidation in air, especially below 1100 degrees C. However, there is little variation between the activation energies for oxidation in air (approximately 279 kJ/m(3)) and in 100% water vapor (approximately 261 kJ/m(3)). Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction show that oxidation of Ti2AlC forms mostly a continuous and stable layer of alpha-Al2O3, along with a thin surface layer of rutile-TiO2 in both environments. However, the thin TiO2 layer volatilizes by forming gaseous TiO(OH)(2) in the presence of water vapor at high temperatures (> 1200 degrees C). At short-term oxidation and lower temperatures, diffusion of hydroxyl ions is proposed to be the rate limiting mechanism under hydrothermal conditions. Above 1100 degrees C, the diffusion of oxide ions through Al2O3 layer becomes the rate limiting step and humidity has little effect on the overall oxidation kinetics of Ti2AlC. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.052202jes] All rights reserved.