By means of FI-IR digital absorbancp subtraction technique the melt quenched PET spectrum was subtracted from those of the PET spectra annealed at different temperatures. By removal of the bands associated with gauche conformation

a series of "trans conformation spectra" corresponding to different crystalline states were obtained.After that

the two "trans conformation spectra" annealed at 240℃ and 120℃ respectively are subtracted each other. The "pure crystalline spectra" and "amorphous trans conformation spectra"are thus calculated. From these differenes spectra

some new bands and the changes of bands of the spectra are found. These results can be explained by the changes of chain rotational conformation associated respectively with crystalline and amorphous region in PET.