A detailed x-ray diffraction study of TiC–ZrC equimolar blend at mechanical alloying in a planetary ball mill is provided. An essential oxidation of carbide components is established. As found, Oxygen from the charge and reaction zone of the mill promotes gradual decomposition of ZrC with the formation of cubic c-ZrO$_{2}$, which further transforms into its monoclinic modification m-ZrO$_{2}$. TiC accumulates the Oxygen in tetrahedral voids of its crystal lattice, forming Ti$_{x}$CO$_{y}$ oxycarbide. Addition of 3% vol. TEG powder to the initial TiC–ZrC charge completely inhibits the oxidation.