This work focuses on modeling of the sorption step as a main step in the mass transport through the pervaporation process. For this purpose, four thermodynamic models including Flory-Huggins (FH), Universal Quasichemical (UNIQUAC), modified Non-Random Two-Liquid (M-NRTL), and modified Wilson (M-Wilson) were used to predict the equilibrium sorption of ethanol/water mixtures into the polydimethylsiloxane (PDMS) membrane. In the M-Wilson model, the reference state based on pure enthalpy of components was used to determine the residual term. Moreover, the influences of ethanol feed content and temperature on the liquid sorption level and sorption selectivity were studied experimentally and theoretically. The results indicated that the proposed models were successfully able to determine the sorption level of the ethanol aqueous solutions into the PDMS membrane. Moreover, the M-NRTL and M-Wilson models were found to be much more accurate than the FH and UNIQUAC models to determine the volume fraction of the penetrants in the PDMS membrane. It was also observed that the total and ethanol sorptions increased with an enhancement in the ethanol feed concentration, while the membrane sorption selectivity decreased. Moreover, increasing the operating temperature led to higher sorption of both ethanol and water, whereas the sorption selectivity did not show significant changes with temperature.