Liquid-liquid equilibrium data of benzoic acid in the systems water + solvent, with tributyl phosphate as extractant and kerosene as diluent, and water + pure 1-octanol are presented. The total benzoic acid concentration in the organic phase increases with an increase of tributyl phosphate concentration, and the extractability of benzoic acid with 1-octanol is equivalent to that with 30 vol % tributyl phosphate in kerosene. Most benzoic acids exist as dimers in the organic phase of tributyl phosphate + kerosene except for the organic phase of pure tributyl phosphate. On the basis of the mass action law and suitable assumptions, the distribution coefficient for benzoic acid with tributyl phosphate is derived, and the apparent equilibrium constants, K-11 and K-12, are evaluated by nonlinear regressions.