Poly(p-dioxanone)-poly(ethylene glycol)-poly (p-dioxanone) ABA triblock copolymers (PEDO) were synthesized by ring-opening polymerization from p-dioxanone using poly(ethylene glycol) (PEG) with different molecular weights as macroinitiators in N-2 atmosphere. The copolymer was characterized by H-1 NMR spectroscope. The thermal behavior, crystallization, and thermal stability of these copolymers were investigated by differential scanning calorimetry and thermogravimetric measurements. The water absorption of these copolymers was also measured. The results indicated that the content and length of PEG chain have a greater effect on the properties of copolymers. This kind of biodegradable copolymer will find a potential application in biomedical materials. (c) 2006 Wiley Periodicals, Inc.