Abstract: AimCharacterization of poly(D,L-lactic acid)/monomethylether terminated/polyethylene glycol （Me.PEG-PLA） block copolymers nanoparticles. MethodsMe.PEG-PLA block copolymers were prepared by bulk polymerization. A series of nanoparticles were made from Me.PEG-PLA block copolymer by modified spontaneous emulsion-solvent evaporation technique. Results and conclusion The structure of copolymer was performed by means of ¹HNMR and FT-IR. The morphological examination of nanoparticles was performed by means of atomic force microscope (AFM). Results indicated that nanoparticles exhibited a smooth spherulite and core-shell structure. The hydrophilic shell is consisted of PEG segments and hydrophobic core is consisted of PLA segments. Zeta potential of nanoparticles was zero and further indicated core-shell structure. The particle size and size distribution of nanoparticles were measured by laser light scattering technique. The effective particle size range was from 70 to 160 nm and showed a normal distribution.