The crystallinity of a glycolysate obtained by glycolysis of PET with diethylene glycol (DEG) was qualitatively studied by optical microscopy using a polarizer and quantitatively by X-ray diffraction. Moreover, the rheological behavior of this glycolysate was also studied in relation with its crystallinity. New glycolysates obtained using oligoesters of different chemical structures as reagents were studied under the same conditions and they show the total absence of crystallinity. According to the structure of the diol or of the oligoester used, the glycolysate crystallinity can be induced or not.