In this investigation, the mutual solubilities and the density of equilibrium liquid phase for ternary o-nitrobenzoic acid-p-nitrobenzoic acid-acetone system were measured at 283.15 K and 313.15 K, respectively. Two isothermal phase diagrams of the system were constructed on the basis of the measured solubilitities, one at 283.15 K and the other at 313.15 K. The phase diagrams of the ternary system were similar at the different temperatures. Two solid-phases were formed and confirmed by Schreinemaker's wet residue method, and the two were identified as o-nitrobenzoic acid and p-nitrobenzoic acid. The crystallization regions of p-nitrobenzoic acid and o-nitrobenzoic acid increase as the temperature decreases. At each temperature, the crystallization of p-nitrobenzoic acid is larger than that of o-nitrobenzoic acid. (C) 2008 Published by Elsevier B.V.