The thermodynamic properties of the liquid Ag-In alloys were determined using solid oxide galvanic cells with zirconia electrolyte. The e.m.f.'s of the cells Re + kanthal, Ag(x)ln((1-x)), In2O3//ZrO2 + (Y2O3)//NiO, Ni, Pt were measured in the temperature range from 950 to 1273 K, and in the molar fraction from x(In) = 0. 15 to 1.0. At first, the Gibbs free energy of formation of pure solid indium oxide, ln(2)O(3), from pure elements was derived. Using values of the e.m.f.'s measured for the cell with x(In) = 1.0, the following temperature dependence was obtained: D(f)G(m,In2O3) (+/- 1000 mol(-1) J) = -911570 + 313.10T Next, the activities of indium were derived as a function of the alloy composition from measured e.m.f.'s. Activities of silver were calculated using Gibbs-Duhem equation. Also, using Darken's alpha-function formalism, activity coefficient of indium at infinite dilution in silver was calculated. These data taken together with the heat of mixing values which are available in the literature enabled the description of the thermodynamic properties of the liquid phase with Redlich-Kister polynomial expansion. Finally, the Ag-In phase diagram was recalculated using ThermoCalc software. The limiting value of the logarithm of the activity coefficient of indium in silver was also given as a function of temperature. (c) 2005 Published by Elsevier B.V.