Trans-3-phenyl-2-propenoic acid (cinnamic acid; trans-cinnamic acid) is widely used in food, cosmetics, and pharmaceuticals because of its reported antimicrobial, antifungal, and antioxidant properties. This paper is devoted to the experimental measurement of the solubility of solid trans-cinnamic acid in pure supercritical CO2 and in supercritical CO2 with ethanol as a cosolvent. Measurements were carried out at T = (313.15 to 343.15) K and at p = (10 to 40) MPa. Two different thermodynamic models were applied to represent the solubility data obtained: a cubic type equation of state, the Soave-Redlich-Kwong (SRK-EoS) was employed to correlate the solubility data and the group contribution associating EoS (GCA-EoS) was also applied but in a completely predictive manner. in addition, values for the thermophysical properties of trans-cinnamic acid are also advocated.