Solubilities of fumaric acid in binary system in supercritical carbon dioxide have been measured as a function of the equilibration time, the acid content in the equilibrium cell, the pressure and the temperature. Mole fraction solubilities of fumaric acid in temperature of 50°C were 6.35×10 -5 at pressure of 80 bar to 3.45×10 -5 at pressure of 300 bar and in temperature of 80°C were 4.1×10 -5 at pressure 60 bar to 0.83×10 -5 at pressure 300 bar. The solubilities are correlated with Peng–Robinson equation of state and Kwak–Mansoori mixing rules. Disagreement of experimental and calculative data shows that the Peng–Robinson equation of state and Kwak–Mansoori mixing rules are not suitable for fumaric acid. The solubilities are correlated with Chrastil equation and association number for fumaric acid was found as 1.226.