We have studied the effect of cryomilling (high-energy ball milling under cryogenic temperature) on the thermal behaviors of poly(ethylene terephthalate) (PET) by comparing with original PET and quenched PET. Cryomilling induced the amorphization of crystalline PET, but the thermal behaviors of amorphous PET obtained from cryomilling are significantly different to those of amorphous PET obtained from quenching. Unlike amorphous PET obtained from quenching, the heating curve of amorphous PET obtained from cryomilling shows no cold crystallization peak, but evidences are found that its cold crystallization occurs within a wide temperature range. In addition, the stability of amorphous PET obtained from cryomilling is higher than that of amorphous PET obtained from quenching. The difference is proved to be attributed to the stored energy in cryomilled PET. The hot crystallization behaviors of PET improve a lot after cryomilling, and the heat stability of cryomilled PET is also better than those of original PET during reheating. (c) 2005 Wiley Periodicals, Inc.