Poly(lactic acid) (PLA) were grafted to both ends of Pluronic F127 (PEO-PPO-PEO) to produce novel amphiphilic PLA-F127-PLA block copolymers. The aggregation behaviors of three different modified polymers were examined by laser light scattering and transmission electron microscopic techniques. The structure of aggregates produced from moderate to long PLA segments (PLAF127-29 (230 units of PLA) and PLAF127-48 (500 units of PLA) systems, respectively) was found to be normal bi-layer vesicles. Polymer with the shortest PLA segment (PLAF127-23 (142 units of PLA)) produces aggregates with complicated onion-like vesicles containing three layers. These vesicles possess microstructure similar to many biological systems, and they exhibit desirable properties for potential applications as drug delivery vehicles.