Temperatures of solid/liquid transitions and vanadium thermodynamic activity data are measured in the U-V system to improve the thermodynamic description of the U-V and C-U-V systems. Binary alloys are synthesized from the pure metals in a high vacuum furnace. With that apparatus, both liquidus temperatures and vanadium activities are measured for each sample. During the experiments, the temperature of the samples is monitored with an optical pyrometer. In parallel, the activity of vanadium referred to pure vanadium is measured for x(V) = 0.18, 0.40 and 0.62 in the (1850 to 2090) K temperature range using high temperature mass spectrometry coupled to a multiple Knudsen cell system. The quenched microstructure of the alloys is analysed by electron microscopy. These new data together with the few ones from the literature are finally used to obtain a consistent set of thermodynamic parameters for the U-V system using the Calphad method. (C) 2010 Elsevier Ltd. All rights reserved.