English abstract The purpose of this experiment is the design and synthesis of a pH-responsive, amphiphilic block copolymers of the low toxicity of the polymer micelles for drug delivery.Amphiphilic biodegradable diblock copolymer of poly(ε-caprolactone) (PCL)-monomethoxy poly(ethylene glycol) (mPEG) was synthesized by ring-opening polymerization of ε-caprolactone with a mPEG as initiator.The doxorubicin was then attached to the PCL terminus via acid-cleavable cis-aconityl. The diblock copolymers were characterized by 1H NMR, FTIR et al. Doxorubicin-conjugated mPEG-PCL diblock copolymers self-assembled to form micelles in aqueous solution,the particle sizes determined by DLS were about 45.4 nm, TEM images showed that these micelles were regularly spherical in shape. The release rate of DOX from micelles at pH 4.0 was observed much faster than that at pH 7.4.The mPEG-PCL copolymer was nontoxic in cell culture, whereas DOX-loaded micelles exhibited time-delayed cytotoxicity in human MCF-7 breast cancer cells. The intracellular localization of free DOX, mPEG-PCL-DOX micelles in MCF-7 were observed by confocal laser scanning microscopy, showed that carrier can take DOX to be entered the cells.