The liquid-liquid equilibrium was measured in the system: water-ethanol-50 wt % solution of tributyl phosphate (TBP) in toluene at 25 degrees C. The parameters of the UNIQUAC model were determined by the method of least squares from experimental tie lines data. The distribution and selectivity curves of ethanol are presented and compared with the curves for the system in which pure TBP is applied as ethanol extractant.