Hydrolytically degradable PET/PEG block copolymer was synthesized by the macromolecular transesterification method from PET and PEG. Non-isothermal crystallization behavior of the copolymers was investigated by differential scanning calorimetry (DSC). Water absorption and in vitro degradation behaviour of these copolymers were studied in detail. When hydrophilic PEG was incorporated into the PET chain, water absorption increased. With the increase in PEG concentration, the degradation rate increased accordingly. PEG molecular weight has different effects on PET/PEG copolymers’ degradation rate. © 2003 Elsevier Ltd. All rights reserved.