Water activity measurements by the isopiestic method have been carried out on the aqueous ternary system of {L-serine + 1-(2-carboxyethyl)-3-methylimidazolium chloride[HOOCEMIM][Cl]} ionic liquid and the aqueous binary system of IL at T = 298.15 K and atmospheric pressure. The data obtained were used to calculate the vapor pressure and osmotic coefficient of solution as a function of concentration. The experimental results for the activity of water were accurately correlated with segment-based local composition models of modified NRTL and UNIQUAC. The fitting quality of the above models has been favorably compared with the NRTL and Wilson models. From these data, the corresponding activity coefficients have been calculated. For the same system, the solubility of the L-serine at various [HOOCEMIM][Cl] ionic liquid concentrations was measured at T = 298.15 K using the gravimetric method. A chemical model was employed to describe the dissociation equilibria of all amino acid species with hydrogen ions in water. Moreover, for L-serine, the chemical model indicated that the formation of cations is insignificant in the [HOOCEMIM][Cl] solution. Also the above local composition models were used to predict the solubility of L-serine in aqueous IL solutions. To provide information regarding (solute + solute) interactions, transfer Gibbs free energies (Delta G(tr)) of amino acid from water to aqueous IL solutions have been determined. (C) 2014 Elsevier Ltd. All rights reserved.