The activities of ethanol and 2-propanol in poly(propylene glycol) 400 (PPG 400) solutions have been measured by the improved isopiestic method at T = (298.15 to 328.15) K. The original equation of Flory-Huggins and the modified Flory-Huggins equation with concentration-dependent interaction parameters have been used for the correlation of the experimental solvent activity data. It was found that for the studied systems at any mass fraction, as the temperature is increased the solvent activities and Flory parameters are both decreased, indicating an increase of interaction between polymer and solvents as the temperature is increased. The reliability of the two local composition models, NRTL and Wilson, was also assessed by fitting the experimental activity data to these models. All of these models satisfactorily present the obtained experimental activity data at different temperatures.