The improved isopiestic method was used to measure 1-propanol activity data for several binary mixtures of 1-propanol + poly(propylene glycol) 400 (PPG400)/poly(propylene glycol) 725 (PPG725)/poly(propylene glycol) 1025 (PPG1025) at 298.15 K. The effect of polymer molar mass was studied on the solvent activity and vapor pressure of the studied systems. The results indicate that solvent activity increases with the increasing of the polymer molar mass. These data have been correlated with different activity models including Flory-Huggins (FH), modified Flory-Huggins, NRTL, NRF-NRTL, Wilson, and NRF-Wilson models. The obtained values of standard deviations for the models represent that modified Flory-Huggins model have good agreement with the experimental data. The apparent specific volume, excess specific volume, isentropic compressibility, isentropic compressibility increments, and apparent specific isentropic compressibility quantities were obtained with use of density and speed of sound data in the 1-propanol + poly(propylene glycol) 400/poly(propylene glycol) 725 systems at T = 288.15 to 318.15 K which supplies the strong solute-solvent interactions and more compatibility between 1-propanol with PPG400 rather than the other Polymers.