In this work the effect of 1-hexyl-3-methylimidazolum bromide on the intrinsic viscosity and some thermodynamic parameters of polyvinyl pyrrolidone in aqueous solutions at 288.15-308.15 K were investigated. The expansion factors of polymer chain were calculated by use of intrinsic viscosity data. The thermodynamic parameters of polymer solution (the entropy of dilution parameter, the heat of dilution parameter, theta temperature and polymer-solvent interaction parameter) were evaluated by temperature dependence of polymer chain expansion factor. The obtained thermodynamic parameters indicate that addition of 1-hexyl-3-methylimidazolum bromide in aqueous solution of polyvinyl pyrrolidone increases thermodynamic quality of water for polyvinyl pyrrolidone. Also thermodynamic quality of solvent for polyvinyl pyrrolidone was decreased by increasing temperature in all systems. (C) 2013 Elsevier B.V. All rights reserved.