A series of polyhedral oligomeric silsesquioxane end-capped poly(spiropyran-containing methacrylate) (POSS–PSPMA) polymers, a kind of photoresponsive hybrid polymer, are synthesized via atom transfer radical polymerization. It is proved that the molecular weight of POSS–PSPMA is sharply increased by raising the proportion of methanol or the concentration of the reactants. The self-assembly behavior of POSS–PSPMA is studied in toluene: under the control of UV and visible light, POSS–PSPMA can reversibly self-assemble into aggregates because the charged merocyanines (MC) form stacks. These MC stacks act as non-covalent crosslinking points and POSS shell guarantees the stability of the aggregates. This system has a broad potential use in nanocarriers, especially for encapsulating and releasing polar substances in the nonpolar solvents.