The solubility of stearic acid in supercritical (SC) CO, with acetic acid + acetonitrile (molar ratio 1:I) and ethanol + acetonitrile (molar ratio 1:1) mixed cosolvents was measured at 318.15 K in the pressure range from 95 to 160 bar, and the total cosolvent concentrations range from 0 to 6 mol%. The density of the fluid phase was also determined, and the effects of pressure, cosolvent concentration, and apparent density of CO, on the solubility have been discussed. The solubility data for the solute in CO, + pure cosolvent binary mixtures was combined. It is known that enhancement of the solubility by the cosolvents follows the order : acetic acid > acetic acid + acetonitrile > acetonitrile, and ethanol > ethanol + acetonitrile > acetonitrile. In other words, the effect of each binary cosolvent on the solubility lies between those of the two pure cosolvents.