The solid-liquid equilibria (SLE) in the ternary system of 2-methyl-1,4-naphthoquinone (2-MNQ) + phthalic anhydride (PA) + 1,4-dioxane were determined experimentally by using the isothermal dissolution equilibriam method within temperatures 283.15, 293.15, and 303.15 K, respectively. The ternary phase diagram could be helpful in the separation of 2-MNQ and PA. On the basis of the experimental data on solubilities the phase diagrams of the system were plotted. 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 Schreinemakers' wet residue method. The phase diagram at 283.15 K is similar to those at 293.15 and 303.15 K and the crystalline regions of 2-MNQ and PA decrease with increasing temperature. NRTL and Wilson model were employed to correlate and calculate the solubility data for the ternary system. A comparison between the two models shows that the NRTL model agrees better with the experimental data than those with the Wilson model. In addition, the densities of equilibrium liquid phase were obtained at the corresponding temperatures versus composition in the system.