The size and size distribution of polymeric nanoparticles have great impact on their physicochemical and biological properties.Polymerization-induced self-assembly(PISA)has been demonstrated to be an efficient method to fabricate various polymeric nano-particles,among which polymeric vesicles have attracted great interest due to their unique hollow structure.However,polymeric vesicles with relatively broad size distributions and random size are normally formed,which is problematic for many potential appli-cations.Herein,we report the synthesis of polymeric vesicles with low-polydispersity and controllable size by polymerization-induced self-assembly.A mixed macro RAFT agent of three different poly(ethylene glycol)(PEGm-CPADB)was used to mediate the RAFT dis-persion copolymerization of 7-(2-methacryloyloxyethoxy)-4-methylcoumarin(CMA)and benzyl methacrylate(BzMA),which generat-ed vesicles with low-polydispersity(＜0.1)and controllable size in the scope of sub-100 nm.In comparison,RAFT dispersion copoly-merization of CMA and BzMA using a single PEG-CPADB as the macro RAFT agent generated vesicles with adjustable but obviously larger size and broader size distributions(＞0.1).The results demonstrate that the ternary stabilizers play a crucial role in the for-mation of small and low-polydispersity vesicles.