The use of polymeric materials as the carrier in the controlled release of guest molecules has become an important research area in the polymeric materials science, because of their advantages of the safety, efficacy and patient convenience. One of them, star amphiphilic polymer can self-assemble into supermolecular structure (polymer micelles) by the balance of hydrophilic and hydrophobic interaction. In this study, star amphiphilic copolymer consisting of hydrophobic and biodegradable poly(E-caprolactone) (PCL) and hydrophilic poly(ethylene oxide) (PEO) blocks were synthesized by two-step ring-opening polymerization. The resultant polymer was characterizated by FTIR, H-1-NMR, and DSC to determine its chemical structure. The morpholoy of the polymer micelles was analyzed by TEM. Using star-PCL-b-PEO as carriers and congo red as model guest molecules, the encapsulation and release properties were investigated by UV-visable analysis. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1372-1379, 2010