Abstract: As part of a study of the isotopic separation of 235U and 200U by chemical exchange, we have determined the single stage isotope separation factor(α) in the isotope exchange systems in which uranyl chloride is extracted by a mac-rocyclic polyether,by means of a stepwise enriching cascade process. For initial U(Ⅵ) concentrations of 5mgU/ml and 100mgU/ml in the aqueous phase, the values of a arc found to be 1. 0010±0. 0002 and 1.0012±0.0004 respectively . The lighter isotope 235U is found to accumulate preferentially in the organic phase containing uranyl polyether complexes. The results of this work indicate that macrocyclic polyether systems yield a higher α than other systems involving no valence change, a fact which is in accord with that found for Li, Na and Ca isotope separation with macrocyclic polyether systems.