Industrial processes for carbon dioxide capture were developed for the treatment of natural gas. They are based on the dissolution of CO2 in aqueous solution of amine. The mechanism is a combination of acido basic reaction and physical dissolution. The thermodynamic representation of the gas-liquid equilibria in {CO2-water-amine} systems is complex [1] as it contains both molecules and ions. To take in account non ideality some interaction parameters can be obtained from binary system such as {water + amine}. However experimental data are scarce except in the case of monoethanolamine (MEA) [2]. In this work the Unifac model [3] was tested for prediction of excess properties of water-amine systems. Some interactions coefficients in the original model were modified using excess enthalpy data of water-MEA. The Unifac model with the new coefficients was tested for prediction of excess properties of different alkanolamines [4] for which experimental data are available in literature.