In this work the intrinsic viscosity of poly(ethylene oxide) was measured in aqueous Solutions of hydrogen chloride at 288.1-313.1 K to investigate effect of temperature and concentration of H3O+ ions. 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 aqueous solutions of hydrogen chloride is changed to the poor solvent for poly(ethylene oxide) by increasing temperature. Aqueous solution of hydrogen chloride in all examined temperatures are changed to the poor solvent for poly(ethylene oxide) by increasing concentration of HCl from 0 to 0.3 M, and aqueous solution of hydrogen chloride is reverted to the good solvent by increasing concentration of HCl from 0.3 to 0.5 M. (C) 2008 Elsevier B.V. All rights reserved.