The technology on the transmutation of nuclear waste has been developed to reduce long-term risks during the storage of the spent nuclear fuels. It was studied on the fluorination of cerium oxide to investigate the preparation of the fuel for transmutation reactor. Cerium oxide was reacted with hydrogen fluoride - hydrogen mixed gas to produce zirconium fluoride in the monel tubular reactor. Cerium oxide powders were converted completely to cerium fluoride in 40minutes at 300℃ and in 25minutes at 500℃. Among the various gas-solid reaction models, the phase boundary controlled model was most suitable for the reaction, it was calculated from the model that 16 hours are required to fluorinate the cerium oxide of 10mm diameter.