The solid liquid equilibrium or the ternary system of 2-methyl-1,4-naphthoquinone + phthalic anhydride + acetone were determined at three temperatures of (283.15, 293.15 and 303.15) K, respectively. Three isothermal phase diagrams of the system were constructed on the basis of the measured solubility. Two pure solid phases were formed at (283.15, 293.15 and 303.15) K, including pure PA and pure 2-MNQ which were confirmed and determined by the method of Schreine makers' wet residue. The densities of equilibrium liquid phase were determined experimentally at the corresponding temperatures versus mass fraction of component. The phase diagram at 283.15 K is similar to those at (293.15 and 303.15) K and the crystalline fields of 2-MNQ and PA decrease with an increase in temperature. The ternary diagram can provide the fundamental basis for separation of 2-MNQ and PA. (c) 2015 Elsevier B.V. All rights reserved.