The structural heterogeneity and molecular motion in a thermoreversible gel consisting of poly(ethylene terephthalate) (PET) and a Liquid ethylene glycol oligomer (PEG) was investigated by solid-state NMR and FT-Raman spectroscopies. PET was dissolved in PEG at elevated temperatures to form a concentrated solution (30 wt %), and the solution formed a gel rapidly on cooling. For the purpose of comparison, a PET/phenol binary system and PET crystallized by annealing methods were also investigated. The longest solid-state NMR relaxation times of C-13 (T-13C(1)) in PET of PET/PEG gel among the samples indicated the slowest molecular motion and the highest rigidity PET chains. The structural heterogeneity of the PET/PEG gel investigated by T-H(1) measurement and confirmed by FT-Raman spectroscopy indicated phase transition during gelation. The crystallinity of PET recovered from polymer/oligomer gels is near 70% as measured by wide-angle X-ray diffraction, which is about 20% higher than that for PET samples crystallized by solution crystallization and high-temperature annealing techniques.