Abstract: Poly(γ-benzyl-L-glutamate)-b-poly(ethylene glycol)-b-poly(γ-benzyl-L-glutamate)(PBLG-b-PEG-b-PBLG) triblock copolymer was synthesized via ring opening polymerization, and characterized by 1HNMR and gel permeation chromatography (GPC). GPC test shows that the polydispersity index (PDI) of the copolymer is very low. The selfassembled aggregates were prepared by dialysis method. The selfassembly behavior of the block copolymer in selective solvent (water) was investigated by transmission electron microscopy, scanning electron microscopy and laser light scattering. The experimental results show that the triblock copolymer can selfassemble into vesicles and micelles. The aggregate structures are found to be dependant on the initial solvent composition and mass concentration of polymers.