The thermal stability of Ti 2 AlC at elevated temperature (1000–1550°C) in vacuum has been investigated using in situ neutron diffraction. At temperatures above 1400°C, Ti 2 AlC became unstable and began to decompose via sublimation of Al, resulting in a porous surface layer of TiC x being formed. The apparent activation energy for Ti 2 AlC decomposition was determined to be 85.7±2.6kJmol −1 . The kinetics of isothermal phase decomposition was modelled using least-squares linear regression fitting and the Avrami equation. The corresponding least-squares regression exponent (R 2 ) and Avrami constants (k and n) for isothermal decomposition were determined to be 0.89, 0.268min −n and 0.1, respectively.