The influence of guest size on the guest exchange behavior of the 6 form of syndiotactic polystyrene was investigated using a series of n-alkanes from n-hexane to n-decane as a guest. The bands due to sorbate and desorbate molecules and the conformational sensitive bands of sPS were followed by ATR-FTIR spectroscopy. The guest exchange of the 6 form containing chloroform proceeded smoothly for all n-alkanes, but it became slow with the length of n-alkane. Although the amount of TTGG helices characteristic of the clathrate structure was kept during the exchange with n-hexane and n-heptane, a decrease in conformational regularity was observed in the beginning of the guest exchange of longer n-alkanes. The absorbed amount of n-alkanes decreased with the amount of the TTGG helices. The frequency shift of the methyl asymmetric stretching band of n-alkanes suggested that the packing of n-alkane molecules in the cavity became tight as the chain length increased.