The mutal solubility and the tie-line data were obtained at 25 ℃ and 1 atm, for ternary and quarternary systems of acetic acid （solute）, water (diluent), and six different solvents. A good linear relationship of the Fujita-Hirata plot was obtaned using those six solvents; 1-butanol, isopropyl ether, and 75 vol %, 50 vol %, 25 vol %, and 10 vol % of 1-butanol in isopropyl ether. The product of the distribution ratio and the selectiviy, M'_A×β_A, was plotted against the volume percent of isopropyl ether to determine the optimum mixing ratio of isopropyl ether which was found to be 69± 2 % by volume.