The non-isothermal crystallization of poly(ethylene terephthalate) (PET) during cooling with constant rates is investigated by differential scanning calorimetry (DSC). The analysis is aided by microscopic investigation of the final morphology. The results are analyzed using the Ozawa model. It is shown that this model describes the non-isothermal process only at relatively low cooling rates. At rates exceeding 20 degrees /min, crystallization progress becomes higher, indicating higher crystallization rates than those resulting from the Ozawa approach. Additional deviation from the Ozawa model observed at the very beginning and the end of crystallization can be attributed to spatial constraints of spherulitic growth. In the first case, the spherulitic growth is impeded by the dense instantaneous nucleation on the polymer surface (transcrystallization) and in the second one by impingements of bulk growing spherulites. (C) 2001 Elsevier Science Ltd. All rights reserved.