Novel sheddable micelles having hydrophilic coronas capable of being shed from biodegradable polylactide (PLA) cores by the cleavage of disulfide linkages in response to thiols were prepared by aqueous micellization of PLA-based amphiphilic block copolymers functionalized with disulfides at block junctions. These well copolymers were synthesized by a combination of ring opening polymerization and atom transfer radical polymerization in the presence of a new disulfide-functionalized double head initiator having both terminal OH and Br groups. (1)H NMR and GPC results indicate that both polymerizations were well-controlled with molecular weight distribution as low as M(w)/M(n) < 1.2. Aqueous micellization to form core/shell micelles with disulfides at the interface of PLA cores and hydrophilic coronas and their thiol-responsive degradation were investigated. In the presence of water-soluble thiols, disulfide linkages in the micelles,were cleaved and hydrophilic coronas were lost, causing PLA cores to precipitate due to the loss of colloidal stability. In a biomedical perspective, the new sheddable micelles were not cytotaxic and hence biocompatible.