Distribution equilibrium of Cu2+ between sulfate solutions and kerosene containing LIX64N was studied. Distribution ratio of Cu2+ increased with increase in the concentration of extractant (10-50 mol/dm(3)) and the initial aqueous pH (1similar to5). A simplified model with three parameters was proposed to describe the equilibrium behavior, in which the non-idealities in both aqueous and organic phases were considered. Under the conditions studied (initial pH 2-5; Cu2+ concentration <10 mol/m(3); LIX64N concentration 10-50 mol/m(3)), it was shown that the results calculated by the present model were in reasonable agreement with the measured ones (standard deviation <12.3%). This model gave a prediction comparable to the one estimated based on Davis equation for correlation of aqueous-phase activity alone, but superior to the one calculated based on the regular solution theory of Hildebrand/Scott for correlation of organic-phase activity alone.