Poly(ethylene glycol)-b-Poly(D,L-lactide) diblock coplymers (PEGDLLAs) were synthesized by ring-opening polymerization of D,L lactide in the presence of methoxy poly(ethylene glycol)(mPEG) as an initiatio. PEGDLLA self-aggregates were prepared by solvent evaporation for hydrophobic drug carrier. The self-aggregation behavior and microscopic characteristics of PEGDLLAs self-aggregates were investigated by 1H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy.