In this study, hydrofluorination of UO2 and CeO2 was carried out at 550 ℃ under the atmosphere of H2 and HF. Uranium dioxide was used as the main constituent of spent oxide fuel and CeO2 used as a surrogate of transuranic oxides. Two hydrofluorination methods were presented: one is a direct hydrofluorination method in a molten fluoride salt and the other is that by gas solid reaction. In the former case, a fluoride mixture of 67% LiF-33% BeF2 was used as carrier molten salt. It was thermodynamically confirmed that UO2 was converted to UF4 and CeO2 to CeF3. As results of the experiments, in the case of UO2, fluorination took place in both systems. In the case of CeO2, however, hydrofluorination in the molten fluoride salt occurred only slightly because of the extremely low solubility of HF and H2 ill the molten fluoride salt. Based on this result, when fluorinating minor actinide oxides in a spent oxide fuel, hydrofluorination by gas solid reaction was predicted to be far superior to that in molten fluoride salt.