Solubility of CO2 in six hydroxyl ammonium ionic liquids 2-hydroxyethanaminium acetate hea, bis(2-hydroxyethyl)ammonium acetate bheaa, 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium acetate hhemea, 2-hydroxyethanaminium lactate hel, bis(2-hydroxyethyl)ammonium lactate bheal, 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium lactate hhemel at temperatures (298.15, 313.15, and 328.16) K and pressures ranging from (100 to 1600) kPa was determined. From the experimental solubility data, the Henry's constant of CO2 for each hydroxyl ammonium ionic liquids was estimated and reported as a function of temperature. Furthermore, enthalpy and entropy of absorption were obtained from estimated Henry's constant. The results showed that the solubility increase with increasing pressure and decrease with increasing temperature and the solubility of CO2 in these six hydroxyl ammonium ionic liquids was in sequence: hea > bheaa > hel > bheal > hhemel > hhemea. © 2009 Elsevier Ltd. All rights reserved.