Surface tension anomalies were observed in room temperature ionic liquid (RTIL)-acetone solutions. The RTILs are 1-alkyl-3-methylimidazorium iodide with [C(n)mim][I] in a [C(n)mim][I]-x mol% acetone. The maximum value of the surface tension appeared at 40 mol% acetone, although density decreased monotonically with an increase in acetone concentration. A small alkyl chain length effect of the C(n)mim(+) cations was observed in the surface tension. By the Gibbs adsorption isotherm, it was found that I - anion-mediated surface structure became dominant above 40 mol%. In the different [C(n)mim][TFSI]-acetone mixtures, normal decay of the surface tension was observed on the acetone concentration scale, where TFSI - is bis(trifluoromethanesulfonyl) imide. (C) 2018 Elsevier B.V. All rights reserved.