Solubility data for the ternary p-nitrobenzoic acid + m-nitrobenzoic acid + ethanol system were measured at 273.1 K, 283.1 K, and 313.1 K, respectively. Three isothermal phase diagrams of the system were Constructed oil the basis of the measured solubilitities. Two solid phases, m-nitrobenzoic acid and p-nitrobenzoic acid, were formed and confirmed by Schreinemaker's wet residue method. The crystallization regions of in-nitrobenzoic acid and p-nitrobenzoic acid increase as the temperature decreases. At different temperature, the crystallization region of p-nitrobenzoic acid is larger than that of m-nitrobenzoic acid.