A well-defined, light-responsive copolymer poly(spiropyrane)-block-poly(ethylene glycol) (PSP-b-PEG) was synthesized by RAFT polymerization. The final copolymer can self assembled into spherical micelles with a hydrophilic PEG corona and a hydrophobic spiropyrane core in aqueous solution. Moreover, the properties of micelles in aqueous solution were detected by fluorescence spectroscopy, UV-vis spectroscopy, dynamic light scattering (DLS), and scanning electron microscope (SEM). Model drug Nile Red was then encapsulated into the micelles and its light-controlled release was studied. In addition, an MTT assay provided the evidence for the low cell cytotoxicity of PSP-b-PEG micelles. The results demonstrate that the spherical micelles of PSP-b-PEG possess a potential application in smart drug delivery.