Physicochemical properties of polyethyleneglycol 8000 (PEG8) and polyethylene glycol 12000 (PEG12) were investigated by means of inverse gas chromatography (IGC) using different groups of solutes as the probes with a different chemical nature were used as eluents. Where the polymers were used as a stationary phases in the chromatographic column. Some thermodynamic parameters, such as specific retention volume, Flory-Huggins interaction, and weight fraction activity coefficient parameter were investigated to judge the interactions between PEG8 and PEG12 with the different solutes. On the other hand the suitability of polymer as a stationary phase was discussed. The ultimatted goal is the prediction of selectivity of these polymers to separate close boiling point and molecular weight solutes (benzene and cyclohexane). The thermodynamic results, indicated that PEG12 more retaind than PEG8 this phenomina apeared due to the effect of molecular weight.