Experimental data are determined for a ternary system, ketoprofen-acetone-water, at various temperatures and atmospheric pressure. Specific procedures are applied. The diagram exhibits five regions : one homogeneous, three two-phase (two liquid-solid and one liquid-liquid equilibria) and one three-phase zones. The variation of the solubility of ketoprofen in acetone-water mixtures is interpreted by analysing the molecular forces induced in the solution according to the acetone mass ratio in the mixture. The validity of semi-empirical models is tested for liquid-solid and liquid-liquid equilibria by comparing the calculated values with the experimental ones. The agreement depends on the precision of the estimated parameters used for calculations.