In this work, the intrinsic viscosities of poly(ethylene glycol) (PEG) with a molar mass of 20 kg . mol(-1) were measured in water-ethanol solutions from (283.1 to 313.1) K. The expansion factors of the polymer chains were calculated from the intrinsic viscosity data. The thermodynamic parameters (entropy of dilution parameter, the heat of dilution parameter, (1 temperature, polymer solvent interaction parameter, and second osmotic virial coefficient) were derived by the temperature dependence of the polymer chain expansion factor. The thermodynamic parameters indicate that mixtures of water-ethanol are changed to the poorer solvents for PEG by increasing temperature. Also the thermodynamic parameters indicate that water-ethanol mixtures are changed to the poorer solvents for PEG by increasing volume fractions of ethanol.