This paper presents a theoretical-experimental study of the metal-mold heat transfer coefficients during horizontal directional solidification of Sn-Pb hypoeutectic alloys (5 wt%Pb, 15 wt%Pb, 20 wt%Pb and 25 wt%Pb) in presence of thermo-solutal convection. A water-cooled solidification experimental apparatus has been developed, and specimens have been solidified under unsteady state heat flow conditions. Five computer guided thermocouples have been connected with the metal, and the time-temperature data have been recorded automatically. A numerical technique which compares theoretical and experimental thermal profiles is used for investigating the influence of solute content on h(i) values. This has permitted the evaluation of the variation of metal-mold heat transfer coefficients along the solidification of Sn-Pb alloys, as well as the analysis of the effects of thermo-solutal convection. The interfacial heat transfer coefficients of alloys studied are represented by equations which show the time dependence during the process. The experimental and calculated values have shown a very good agreement. A comparative analysis between the results of this work and those from the literature proposed to analyze the metal-mold heat transfer coefficients during upward and downward vertical solidification of Sn-Pb hypoeutectic alloys is conducted. (C) 2011 Elsevier B.V. All rights reserved.