The conversion ratio of UO₂ to UCl₄ was 97.9% at 2 hour and reached to 99.7% at 3 hour of reaction time. The volatilization ratio was sharply increased from 39.7% to 73.2% as reaction time goes 2 to 3 hours. Also, the conversion ratio was gently increased in the range of 400℃∼700℃ whereas over 700℃ it was relatively slight and the volatilization was sharply increased over 700℃. The optimum injection rate of the carrier gas is about 50% of that of reacting gas and 140% of equivalence point of reductant based on reaction mechanism was appropriate for the chlorination of UO₂ to UCl₄ in reaction system. Finally, the equivalence point of reacting gas based on reaction mechanism was proper in conversion and volatilization.