Host-guest complexation between ionic liquid (IL) 1-butyl-3-methylimidazolium octylsulphate [Bmim] [OS] and cyclodextrins (alpha- and beta- CDs) have been studied. Surface tension, conductivity measurements revealed the formation of 1: 1 (M) stoichiometry for inclusion complexes (ICs) and further confirmed by UV-Visible and FT-IR results. The nature of the complexes has been established using interfacial and thermodynamic parameters. The aggregation number, Stern-Volmer constants, association constants were obtained from fluorescence quenching and Benesi-Hildebrand methods. The critical micelle concentration (cmc) and association constants of [Bmim][OS] are higher for beta-CD as compared to alpha-CD. FT-IR spectra indicated that CDs and [Bmim][OS] could from ICs with stoichiometry 1: 1 (M). (C) 2017 Elsevier B.V. All rights reserved.