A number of studies have been carried out on the separation of uranium ion by using solid-supported membranes and solvent polymeric membranes. However, the content of carrier solvent decreased and the quality of the membrane deteriorated with operation time. The present study is aimed at of the development of long-life polymeric membranes with improved stability. In this work, the cellulose triacetate(CTA) membrane containing tri-n-octylphosphine oxode(TOPO) were prepared by the phase inversion method. In this membranes, TOPO particle can act as a carrier when they are contacted with nitric acid by its gelation. The dominating factors controlling the membrane properties in the preparation process were found to be the amounts of plasticizer, CTA/TOPO ratio, and evaporation time. As a results of another experiment, the permeation rates showed constant value during a 30 day experiment, which means the excellent stability of TOPO-CTA membrane. This preliminary study has demonstrated that these membrane seems to be a promising means for separating uranium contained in aqueous solution. (Author).