The extraction equilibrium of cerium(IV) and fiuoriue(l) from II2SO4 solution tyCyanex 923 was studied. The extraction mechanism of Ce(IV) and F(I) by Cyanex923 was determined by the method of slope analysis. The results showed that Cyane923 can extract HF as HF.L and Ce4+ together with HF as Ce(HF)(HSO4)2(SO4).2Lby which HF comes into the organic phase mainly when there is Ce4+ in the solution,where L is the extractant. Temperature did not affect the extraction. The IR spectraof purified Cyanex 923 saturated with Ce(IV) and HF were discussed.``