Aqueous solubility of acetaminophen in the presence of 1-hexyl-3-methyl imidazolium bromide, ionic liquid as co-solvent was investigated at different temperatures and mass fraction of ionic liquid. The obtained results reveal that the solubility of acetaminophen was increased by increasing temperature and concentration of ionic liquid. Thermodynamic functions of dissolution, mixing and transfer process were calculated by Van't Hoff equation. The experimental solubility of acetaminophen was correlated with the Wilson and NRTL models as activity coefficient model. The obtained average relative deviations indicate that the experimental solubility of acetaminophen in aqueous ionic liquid solution has a good correlation with the Wilson and NRTL models. (C) 2016 Elsevier B.V. All rights reserved.