The sorption behavior of polyethylene terephthalate (PET) were studied using Inverse Gas Chromatography in a wide range of temperature. PET was used as a stationary phase in a column. Four kinds of alcohols were used as the mobile phase, in other words, probe, namely ethanol, n-propanol, n-butanol, and n-pentanol. Ortho-chlorophenol, a good solvent for PET, was also used as a probe. The value of Vg (specific retention volume) and S (sample size)-Vg relation were investigated.In PET-alcohol systems, below 100°C, two distinct regions for Vg behavior were observed. At the lower probe concentration Vg decreased markedly with increasing S and at the higher concentration Vg increased linearly with S. Above 100°C, Vg decreased with increasing S.In PET-o-chlorophenol system, Vg decreased markedly and linearly with increasing S at the lower and higher concentration, respectively.Limiting specific retention volume, V°g, was estimated by extrapolating the S-Vg relation to S=O. A relationship between ln V°g and 1/T was discussed.The sorption isotherms were determined from the peak profile. The sorption behavior of two systems were analysed using the sorption isotherms, B. E. T. plot, Flory-Huggins χ parameters.It is concluded from these results that the PET-alcohol system is a solution type and the PET-o-chlorophenol system is both solution and B. E. T. types.