The effects of co-solvent to the solubility of ginger bioactive compounds, 6-gingerol, 6- shogaol, 8-gingerol and 10-gingerol in hot water were calculated using the conductor-like screening model for real solvent (COSMO-RS). In this work, ethanol was used as the co-solvent. The σ- profiles of the molecules were calculated using Gaussian software and the solubility were calculated using the COSMO-RS method. The solubility of these ginger bioactive compounds were calculated at 50 to 150°C.The amounts of ethanol used were 0 mol (binary system), 0.005, 0.010 and 0.015 mol. The results show that when the concentration (mole fraction of ethanol) of co-solvent increases, the solubility of ginger bioactive compounds increase. While the temperature increases, the concentration (mole fraction of ethanol) of co-solvent decreases.