This work presents an experimental investigation on the heat transfer characteristics of a cooled vertical turbulent flow of supercritical carbon dioxide. The test section consists of two sectors (vertical tube-in-tube) connected in series by means of a U-bend. An integral method is used to treat the experimental data. Experimental results illustrate the influence of buoyancy forces on the heat transfer process. Results are presented in dimensionless form commonly used in the studies of mixed convection in heating. Correlations have been developed for upward and downward flows. The present results complete the literature on turbulent vertical mixed convection under cooling conditions. (C) 2009 Elsevier Ltd. All rights reserved.