Abstract This work aims at understanding the oxidation mechanism of a TiC–SiC nanocomposite ceramic material. Samples were subjected to heat treatments up to 1400°C under air, varying the relative density of the composite, the heating rate, and the dwell time. The weight variations were followed by thermogravimetric analyses coupled with mass spectrometry. The oxidized samples were then characterized by scanning electron microscopy on cross‐sections (SEM‐EDX) and their microstructure and composition were studied by transmission electron microscopy (TEM‐EDX). The oxidation process was also followed by in situ high‐temperature X‐ray diffraction and high‐temperature environmental scanning electron microscopy. Until 1000°C, the formation of a multilayer alteration scale was observed, with a dense and protective SiO 2 layer. Above 1200°C, this layer showed cracks, and the oxidation was increased. Based on the results, a three‐step mechanism was proposed for the temperature‐dependent conversion of TiC and SiC to the subsequent oxides.