In this study the oxidation resistance of Ti-45Al-8Nb (at.%) alloy coated with quaternary Ti-Al-Cr-X layers (X = Si, Hf, Y, Zr and W) was investigated. The Ti-Al-Cr-Si, Ti-Al-Cr-Hf and Ti-Al-Cr-Y coated specimens were exposed to air at 950°C under cyclic conditions, whereas the samples with Ti-Al-Cr-Zr and Ti-Al-Cr-W coatings were thermally cycled at 1000°C. After the maximum exposure time period of 1000 1h-cycles or failure cross-sections of the samples were examined by means of SEM and EDS to analyse the microstructural evolution. At initial stages of exposure, all intermetallic layers formed a thin alumina layer on top, providing a diffusion barrier to oxygen. But interdiffusion between coating and substrate caused depletion of the Ti(Cr,Al)₂ Laves phase in the intermetallic layers, which promoted the formation of alumina, as well as transformation into Ti-rich B2-phase. Coarsening of the latter phase beneath the alumina scale resulted in a higher oxidation resistance compared to that of ternary Ti-Al-Cr coating.