Abstract: The isotope separation effect of uranium by extraction with dicyclohexyl-24-crown-8(DCH24C8) has been studied. The single stage separation factor (α) is determined in the isotope exchange systems,in which uranyl chloride is extracted by DCH24C8 involving no change of uranium valency. By means of a stepwise enriching and depleting cascade process,the values of a are found to be 1. 00061±0. 00009 and 1. 00066±0. 00019,respectively,for the initial U(Ⅵ) concentration of 0. 31 mol/1 in the aqueous phase at 27℃. The lighter isotope 235U is found to accumulate preferentially in the organic phase containing uranyl polyether complex.