Anionic diblock copolymers (P(m)A(n)) composed of biocompatible polybetaine, poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC), and anionic poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PAMPS) were synthesized via reversible addition fragmentation chain transfer (RAFT) radical polymerization. Two types of diblock copolymers (P(242)A(217) and P(100)A(99)) were prepared with different compositions. The P(m)A(n) CTAB complexes were formed by a stoichiometrically charge neutralized mixture of anionic P,A and cationic cetyltrimethylammonium bromide (CTAB) micelles in water. The complexes prepared using P(24)A(217) and P(100)A(99) were vesicles and micelles, respectively, and were covered with hydrophilic PMPC shells. The complexes dissociated upon addition of NaCI because the complex was maintained through electrostatic interactions. The P(24)A(217)/CTAB vesicles could encapsulate uncharged hydrophilic guest molecules into the interior of the aqueous phase.