Controlled morphologies of aqueous sheddable block copolymer aggregates having tunable thiol-responsive degradation are reported. New thiol-responsive degradable block copolymers consisting of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic polystyrene (PSt) block having disulfide linkages at block junctions were synthesized by atom transfer radical polymerization in the presence of a newly-synthesized PEO-based bromine macroinitiator labeled with disulfides. These well-controlled PEO–ss–PSt block copolymers self-assembled to form aqueous aggregates having various morphologies, including spheres, vesicles, and rod-like aggregates, which was controlled not only by structural parameters, such as PSt block length and disulfides, but also by using the aqueous micellization method. Such structural and morphological variation of aqueous aggregates led to the control of their thiol-responsive degradation rate.