Corundum-type (AlxCr1−x)2O3 coatings were grown by reactive cathodic arc evaporation in an oxygen atmosphere using AlCr targets with an Al/Cr atomic ratio of 1. Since the (AlxCr1−x)2O3 solid solution shows a miscibility gap below 1300°C, where spinodal decomposition is predicted, the microstructural changes upon annealing were investigated by a combination of transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. The as-deposited coating consists primarily of the corundum-type (AlxCr1−x)2O3 solid solution, with smaller fractions of cubic (AlxCr1−x)2O3. An additional Al-rich amorphous phase and a Cr-rich crystalline phase stem from the droplets incorporated. The corundum-type (AlxCr1−x)2O3 solid solution is still present after vacuum annealing at 1050°C for 2h, whereas the cubic (AlxCr1−x)2O3 phase has transformed to corundum-type (AlxCr1−x)2O3. Cr and Cr2O3 have been detected in the annealed coating, the latter most probably originating from the partial oxidation of Cr-rich droplets. Upon crystallization of the amorphous phase fractions present, γ-Al2O3 is formed, which then transforms into α-Al2O3. No evidence for decomposition of the corundum-type (AlxCr1−x)2O3 solid solution could be found within the temperature range up to 1400°C.