Activity coefficients and diffusivities of small molecules in phenol resin were determined by using inverse gas chromatography (IGC) technique with packed column. The Romdhane-Danner approach was used to measure the diffusivities for solvents in phenol resin. Since the thickness of the polymer film on the support materials has a significant effect on the value of diffusivity, it was determined by using a more accurate method based on Braun-Guillet approach. The experimental data of activity coefficients and diffusivity at infinite dilution for three systems have been determined. The PolyNRTL model was adopted to represent the measured activity coefficient data. Also, the elution model of the packed columns and the estimations of model parameters were evaluated to obtain the diffusivity.