Vinyl sulfone-terminated polyethylene glycol-poly(L-lactide) (VS-PEG-PLLA) diblock copolymer was designed as an amphiphilic structure containing a VS group with high reactivity toward thiols. Prior to the copolymer synthesis, heterobifunctional PEG with a VS group at one terminus was prepared and then PLLA was introduced to the other end of PEG. The chemical structure and molecular weight of the resulting products was assigned by H-1 NMR and GPC. As micellar properties of VS-PEG-PLLA under aqueous environment, the critical micelle concentration and mean size of VS-PEG-PLLA were found to be approximately 59.8 mg/L and 34 nm, respectively. Kinetic studies of the VS-functionalized PEG-PLLA micelle showed that the reaction rates were affected by various factors but most of cysteine-contained peptides reacted rapidly within I h via Michael-type addition. Therefore, this thiol-reactive polymeric micelle is expected to be very useful for it functional nanocarrier system through the effective conjugation of cysteine-containing peptides or proteins.