Star oligo/poly(2,2-dimethyltrimethylene carbonate)s containing cholic acid moieties were synthesized through the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) initiated by cholic acid with hydroxyl groups. Through the control of the feed ratio of the initiator cholic acid to the monomer DTC, a series of star oligomers/polymers with different molecular weights were obtained. The star oligomers/polymers were characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, combined size exclusion chromatography/multi-angle laser light scattering analysis, wide-angle X-ray scattering, polarizing light microscopy, and differential scanning calorimetry. Compared with linear poly(2,2-dimethyltrimethylene carbonate), these star oligo/poly(2,2dimethyltrimethylene carbonate)s had much faster hydrolytic degradation rates. With one of the star oligomers/polymers, a microsphere drug-delivery system of a submicrometer size was fabricated with a very convenient ultrasonic dispersion method that did not involve toxic organic solvents. The in vitro drug release was studied. (c) 2006 Wiley Periodicals, Inc.