Water activity of the mixed aqueous solutions, {L-serine + 1-butyl-3-methylimidazolium bromide, [C(4)mim][Br]} have been measured by the isopiestic method at temperature 298.15 K. The behaviour of constant water-activity lines were used to obtain some information regarding salting effect of the ionic liquid on the aqueous L-serine solutions. The experimental results for the activity of water were accurately correlated with segment-based local composition models of the Wilson, NRTL and modified NRTL. The parameters obtained from these models were adopted to calculate the corresponding activity coefficients. For the same system, the solubility of the L-serine at various ionic liquid (IL) concentrations was measured at T = 298.15 K using the gravimetric method. Also the above local composition models were used to predict the solubility of amino acid in pure water and in aqueous IL solutions. To provide information regarding ( solute + solute) interactions, Gibbs free energies (Delta(transfer)G) 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 {[C(4)mim][Br] + water} solutions which have been calculated from different models, as a function of IL concentration at T = 298.15 K. Furthermore, the difference between salt effects of [C(4)mim][Br] and two previously studied carboxylic ionic liquids were discussed. (C) 2014 Elsevier Ltd. All rights reserved.