Abstract: High-temperature oxidation behavior of ferrovanadium (FeV₂O₄) and ferrochrome (FeCr₂O₄) spinels is crucial for the application of spinel as an energy material, as well as for the clean usage of high-chromium vanadium slag. Herein, the nonisothermal oxidation behavior of FeV₂O₄ and FeCr₂O₄ prepared by high-temperature solid-state reaction was examined by thermogravimetry and X-ray diffraction (XRD) at heating rates of 5, 10, and 15 K/min. The apparent activation energy was determined by the Kissinger–Akahira–Sunose (KAS) method, whereas the mechanism function was elucidated by the Malek method. Moreover, in-situ XRD was conducted to deduce the phase transformation of the oxidation mechanism for FeV₂O₄ and FeCr₂O₄. The results reveal a gradual increase in the overall apparent activation energies for FeV₂O₄ and FeCr₂O₄ during oxidation. Four stages of the oxidation process are observed based on the oxidation conversion rate of each compound. The oxidation mechanisms of FeV₂O₄ and FeCr₂O₄ are complex and have distinct mechanisms. In particular, the chemical reaction controls the entire oxidation process for FeV₂O₄, whereas that for FeCr₂O₄ transitions from a three-dimensional diffusion model to a chemical reaction model. According to the in-situ XRD results, numerous intermediate products are observed during the oxidation process of both compounds, eventually resulting in the final products FeVO₄ and V₂O₅ for FeV₂O₄ and Fe₂O₃ and Cr₂O₃ for FeCr₂O₄, respectively.