Thermal analysis based on TGA (thermal gravimetric analysis) and DSC (differential scanning calorimeter) shows no significant degradation for PVDC which has been annealed at 210 degrees C for less than 2 min. And the following recrystallization behavior at lower temperature (120 degrees C) is also independent of the thermal treatment and is not affected by the difference of molecular weight. The degradation which includes dehydrochlorination at lower temperature and intramolecular cyclization or intermolecular crosslinking of the polyenes at higher temperature starts when the melting time at 210 degrees C is more than 2 min, which also causes weight loss and heat exchange in the TGA and DSC thermograms. The recrystallization behavior of the degraded PVDC (staying at 210 degrees C for more than 2 min) shows a strong dependence on the molecular weight. The crystallinity is decreased with the melting time at 210 degrees C due to the increase of the degree of crosslinking. However, the POM (polarized optical microscopy) pictures and IR spectra show a favorable nucleation effect is present due to the formation of trichlorobenzene from the cyclization of the polyenes as nuclei. The crystallinity of the PVDC recrystallized at 120 degrees C after staying at 210 degrees C for more than 2 min is actually dependent on the molecular weight, melting time at 210 degrees C, and cyclized or crosslinking types of degradation.