In this study, in vitro degradation behavior in buffer solutions of poly(sebacic anhydride-co-ethylene glycol), synthesized with sebacic acid and poly(ethylene glycol) (PEG) via melt-condensation process, was investigated. These copolymers degraded in a surface layer erosion mode within 300 mum from the edge of polymeric matrix that differs from that of neat poly(sebacic anhydride) (PSA), which exhibits simple surface erosion behavior. On the early stage of degradation, synthesized copolymers lost more weight than neat PSA, due to the loss of hydrophilic PEG segments located near surface layer of the polymeric matrices. However, because of the enhanced crystallinity of sebacic anhydride chain segments by the introduction of soft PEG chain segments, degradation rates of copolymers were slower than neat PSA at later stages after 96 h. In addition, degradation rate of copolymeric matrix was determined by the degradation of sebacic anhydride chain segments, which protect PEG chain segments located in the inner part of copolymeric matrices. (C) 2004 Published by Elsevier B.V.