The vapor pressure of mercury over molten Hg-In alloys was measured, and the results were used for the activity determination. Thermodynamics assessment of the Hg-In binary system was conducted using the Calphad approach based on the experimental results determined in this study as well as those found in the literature. The Hg-In phase diagram was calculated using assessed thermodynamic models. It was found that the calculated thermodynamic properties and phase diagram are in good agreement with the experimental data. (C) 2009 Elsevier B.V. All rights reserved.