This paper delineates the change in aggregation behavior of aqueous sodium dodecylsulfate (SDS), an anionic surfactant upon addition of "hydrophilic" ionic liquid (IL) 3-methy-1-pentylimidazolium tetrafluoroborate in an increase in critical micelle concentration (cmc). The results demonstrate the presence of electrostatic and hydrophobic interactions between the ions of IL and the head group of the surfactant. From the cmc values and their temperature dependence, the thermodynamic parameters, viz, free energy of micellization (Delta G(m)(0)) and entropy of micellization (Delta S-m(0)) were evaluated to permit speculation of the interactions existing in the studied aqueous surfactant-IL systems. Further, (HNMR)-H-1 chemical shift measurements in micelle solutions containing IL have also been carried out. The results obtained are compared with the conclusions drawn from the conductance and fluorescence measurements. (C) 2013 Elsevier B.V. All rights reserved.