Novel photoresponsive amphiphilic copolymers, poly{methoxy[oligo(ethylene glycol)] methacrylate-co-styrene}, were synthesized using a spirobenzopyran initiator by atom transfer radical polymerization. The spiropyran and merocyanine forms of the spirobenzopyran moiety at the end group successfully underwent photoisomerization under the conditions of micelle formation, which resulted in a drastic change in micellar properties, e.g., in the assembly state and the hydrophobic environment.