Water activity measurements by isopiestic method have been carried out on the aqueous solutions of alanine + tri-potassium citrate (K(3)Cit) over a range of temperatures at atmospheric pressure. From these measurements, values of the vapor pressure of solutions were determined. The effect of temperature on the vapor-liquid equilibrium of alanine + K(3)Cit + H2O systems has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson and NRTL models. The agreement between the correlations and the experimental data is good. (C) 2008 Elsevier B.V. All rights reserved.