The solubility of aspirin in supercritical CO2 (SC-CO2) with stearic acid as a co-solvent was measured at various pressures and temperatures. The experimental data were obtained by a static method. Stearic acid had a significant effect on the enhancement of solubility, as the aspirin solubility increased by up to 16 times. Further, the effect of stearic acid on the solubility enhancement of aspirin was compared with that of other co-solvents. Different semi-empirical models from the literature were applied for correlating the experimental data, proving good agreement with the experimental data. The model of Sung and Shim exhibited the lowest deviation from the obtained data. The results of the solubility test can be employed to produce aspirin-based pharmaceuticals using supercritical fluid technology (SFT).