—The surface tension (σ) and density (ρ) of indium–tin melts are measured by various methods. The surface tension is measured by the sessile drop method and the method of the maximum pressure in a drop, and the density is measured by an aerometer and the sessile drop method. High-purity metals, In-00 and OVCh tin, are used for this research. The maximum σ measurement error is 0.8% and that of ρ is 0.2%. The composition dependence of σ of In–Sn melts is characterized by an extreme (flat minimum) in the region of the equimolar composition. As the temperature increases, the depth of the minimum decreases and its position shifts toward pure indium. The molar volumes have small positive deviations from the additive values. The sessile drop method is used to measure the temperature dependences of σ and ρ of In–Sn solutions diluted with indium. Indium additives are shown to decrease the surface tension of tin. Since the surface tension of indium is higher than that of tin, this result indicates that the surface tension isotherms of the indium–tin system should pass through a minimum.