Polyvinyl pyrrolidone, a nontoxic biocompatible polymer, has broad applications in pharmacy, cosmetics, and detergent industry. Although PVP is easily soluble in water, some recent findings indicate that water is not a thermodynamically good solvent for PVP. In this research, interaction of PVP with 1-butyl-3-methylimidazolium bromide ionic liquid was studied via FT-IR, UV-vis and viscometric methods. The flow activation energies were found from the linearization of Arrhenius equation and correlated in terms of polymer concentration. Thermodynamic quality of solvent was investigated using the sign of initial slope of the activation energy versus polymer concentration at zero concentration. For this purpose, viscosity and density of polyvinyl pyrrolidone in aqueous solution of ionic liquid at the temperature range of 288.15-313.15 K were measured. Results suggested that the thermodynamic quality of water is increased by addition of 1-butyl-3-methylimidazolium bromide in aqueous solution of polyvinyl pyrrolidone. (C) 2015 Elsevier B.V. All rights reserved.