The isothermal oxidation behavior of Cr 2 AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410°C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr 2 AlC films form a dense continuous oxide scale consisting of α-Al 2 O 3 on Cr carbides. The oxidation rates determined by thermo gravimetric analysis (TGA) were parabolic, indicating that diffusion through the scale is the rate limiting mechanism. The activation energy for oxidation was determined to be 348kJmol −1 and the parabolic rate constant at 1230°C was 7.1×10 −10 kg 2 m −4 s −1 . Hence, the oxidation behavior is comparable to NiAl in the temperature range and time intervals investigated. With increasing oxidation time voids form at the interface between oxide and Cr carbides and the amount of Cr 7 C 3 increases at the expense of Cr 3 C 2 . Based on our thermodynamic calculations the oxygen partial pressure below the oxide scale increases as Al is depleted and Cr carbides oxidize, resulting in CO gas- and Cr 2 O 3 -formation. The formation of gas may together with the depletion of Al and Cr lead to the significant void formation observed in the Cr carbide interlayer. Observation of both Cr carbide precipitates and the formation of (Al,Cr) 2 O 3 solid solution support this notion. For comparison bulk Cr 2 AlC was oxidized. It is argued that the absence of pores in oxidized bulk Cr 2 AlC is due to the considerably larger amount of Al available.