Abstract: This paper describes the kinetics of the U(Ⅵ)-U(Ⅵ) heterogenuous isotope exchange reaction between the extracted complex of the macrocyclic polyether-U(Ⅵ)in dichloroethane continuous phase and uranyl ion in aqueous phase by a falling single drop technique which is often used to study the kinetics of liquid-liquid extraction. The results of the study show that the rate law is consistent with first-order reaction. The time for 50％ exchange is about 9.3 seconds when the radii of the liquid drops are about 0.156cm.