Starch and poly(p-dioxanone) (PPDO) are the natural and synthetic biodegradable and biocompatible polymers, respectively. Their copolymers can find extensive applications in biomedical materials. However, it is very difficult to synthesize starch-graft-PPDO copolymers in common organic solvents with very good solubility. In this article, well-defined polysaccharides-graft-poly(p-dioxanone) (SA(n)-PPDO) copolymers were successfully synthesized via the ring-opening polymerization of p-dioxanone (PDO) with an acetylated starch (SA) initiator and a Sn(Oct)(2) catalyst in bulk. The copolymers were characterized via Fourier transform infrared spectroscopy, H-1 NMR, gel permeation chromatography, thermogravimetric analysis (TG), differential scanning calorimetry, and wide angle x-ray diffraction. The in vitro degradation results showed that the introduction of SA segments into the backbone chains of the copolymers led to an enhancement of the degradation rate, and the degradation rate of SA(n)-PPDO increased with the increase of SA wt %. Microspheres with an average volume diameter of 20 mu m, which will have potential applications in controlled release of drugs, were successfully prepared by using these new copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5344-5353, 2009