Carboreduction of UO₃ has been studied by in situ infrared spectroscopy in order to detect the presence of carbon monoxide during the reduction. From thermogravimetry, the reaction was observed to occur in two steps: (i) Reduction of UO₃ to U₃O₈ by carbon at 440°C and (ii) reduction at 590°C of U₃O₈ to UO₂₃ by carbon. No carbon monoxide was observed during the reaction. Nevertheless, formation of carboxylate species is observed at temperature below 550°C with absorption bands at 1017 and 1300 cm^-1.