Abstract Surface tensions of InSn liquid alloys of various compositions were measured at high temperatures. The measurement was carried out by means of a maximum bubble pressure method. Paying particular attention to the effect of 2-butanol vapor adsorption upon the surface composition C 1 s in addition to inert gases, 2-butanol vapor was used to make the bubble. The experimental results revealed that the adsorption of 2-butanol vapor results in a great deviation of the surface composition from the bulk composition C 1 b. In addition, the C 1 s- C 1 b relation was found to exhibit an S-shaped curve with a singular point defined by C 1 s = C 1 b ⋟ 0.5 . At this point, the adsorption coefficient K a for 2-butanol was found to take a maximum value. The formation of a small amount of a complex having the composition of In Sn ⋟1 is discussed, and an especially strong interaction of the complex with 2-butanol is suggested.