Vapor-liquid equilibrium data (water activity, vapor pressure and osmotic coefficient) of the mixed aqueous solutions, L-threonine+ 1-carboxymethyl-3-methylimidazolium chloride and the corresponding binary aqueous amino acid solutions have been measured by the isopiestic method at temperature 298.15 K and atmospheric pressure. The experimental data for the activity of water were accurately correlated with segment-based local composition models of the Wilson, NRTL, modified NRTL and NRF-NRTL. From these data, the corresponding activity coefficients have been calculated. For the same system, the solubility of the L-threonine at various ionic liquid (IL) concentrations was measured at 298.15 K using gravimetric method. Also the above local composition models were used to describe the solubility of amino acid in pure water and 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 from the solubility measurements and activity coefficient of amino acid in water and [Cmmim][Cl] + water solutions calculated from different models, as a function of IL concentration at 298.15 K. (C) 2014 Elsevier B.V. All rights reserved.