Kinetics studies on the extraction of Zr and Hf using the mixture of diisobutyl ketone (DIBK) and trioctylphosphine oxide (TOPO) as extractant were performed in a Lewis Cell. The results showed that the extraction rate of Zr was governed by chemical reaction in the bulk phase. The extraction rate of Hf was controlled by chemical reaction and mass diffusion at the interface. It testified that the overall extraction reaction was an exothermic and non-spontaneous process, which occurred via an S(N)2 mechanism. Under the given conditions, the overall extraction rate equation and rate-limiting chemical reaction step of Zr and Hf were proposed.