Biodegradable amphiphilic graft copolymers poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide]-g-poly(epsilon-caprol actone) (PHEA-g-PCL) with different branch lengths were synthesized through the ring-opening polymerization of epsilon-caprolactone initiated by the macroinitiator PHEA bearing hydroxyl groups. With use of the graft copolymers with different compositions, nanoparticle drug delivery systems with sizes smaller than 100 nm were prepared by a dialysis method, and microparticle drug delivery systems with sizes smaller than 5 Am were fabricated by a melting-emulsion method. The regularly spherical shapes of the drug-loaded nano- and microparticles were verified by transmission electron microscopy and scanning electron microscopy. In vitro drug release properties of nano- and microparticle drug delivery systems were investigated, with the emphasis on the effects of polymer composition, particle size, and drug-loading content on the release behaviors.