A series of biodegradable amphiphilic graft polymers were successfully synthesized by grafting poly (2,2-dimethyltrimethylene carbonate) sequences onto a water-soluble polymer poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide] (PHEA) backbone. We established the feasibility of preparing these novel graft polymers by the ring-opening polymerization initiated by the macroinitiator PHEA bearing hydroxyl groups without adding any catalyst. The successful grafting of poly(2,2-dimethyltrimethylene carbonate) sequences onto the PHEA backbone was verified by combined size exclusion chromatography and multi-angle laser light scattering analysis. The chemical structures of graft polymers were characterized by Fourier transform infrared and H-1 NMR. By controlling the feed ratio of the monomer to the macroinitiator graft polymers with different hydrophilicities can be easily obtained.