Activity coefficients of CaCl2 in disaccharide {(maltose, lactose) + water} mixtures at 298.15 K were determined by cell potentials. The molalities of CaCl2 ranged from about 0.01 mol . kg(-1) to 0.20 mol . kg(-1), the mass fractions of maltose from 0.05 to 0.25, and those of lactose from 0.025 to 0.125. The cell potentials were analyzed by using the Debye-Huckel extended equation and the Pitzer equation. The activity coefficients obtained from the two theoretical models are in good agreement with each other. Gibbs free energy interaction parameters (g(ES)) and salting constants (k(S)) were also obtained. These were discussed in terms of the stereo-chemistry of saccharide molecules and the structural interaction model. (c) 2007 Elsevier Ltd. All rights reserved.