The solubilities of p-nitrobenzoic acid in supercritical carbon dioxide and carbon dioxide + cosolvents were determined at (308, 318, and 328) K and over the pressure range from (8.0 to 21.0) MPa. The effect of cosolvents, cyclohexane, ethanol, cyclohexane + acetone (equal-molar mixture), and acetone on the solubility of p-nitrobenzoic acid was studied at a mole fraction of 3.0 % (cosolvents in supercritical mixtures). The solubility data in supercritical carbon dioxide in the absence and presence of cosolvents were correlated by the equations proposed by Mendez-Santiago and Teja with satisfactory agreement, respectively.