By using the improved isopiestic method, solvent activity measurements have been performed on the systems poly(ethylene glycol) 400 (PEG 400) + 1-propanol and 1-butanol at 298.15 K. Calcium chloride was used as the isopiestic standard for the calculation of activities. The obtained solvent activity data were correlated with the original Flory-Huggins model. The strength of interaction between different alcohols and the polymer was discussed on the basis of the obtained Flory-Huggins interaction parameters. Measurement of the density, speed of sound, and viscosity data were also performed at T = (288.15 to 328.15) K for the PEG 400 + 1-propanol and 1-butanol systems. The excess molar volume, V-E, isentropic compression deviation, Delta K-s, and viscosity deviation, Delta eta, have been calculated for each composition from the experimental data and fitted to the Redlich-Kister equation.