Because of the advantageous properties, the photoresponsive bioinspired polymers are of great interest for many applications. In this study, we synthesized a new family of photoresponsive poly(ethylene glycol)-block-poly(o-nitrobenzyl-L-glutamate) diblock copolymers, which can self-assemble into spherical micelles in aqueous solution. Upon UV irradiation, an interesting photoinduced morphology transition from spheres to cylinders was observed arising from the disruption of amphiphilicity induced by the cleavage of o-nitrobenzyl groups on the side chains. A couple of techniques including proton nuclear magnetic resonance (H-1 NMR) and ultraviolet-visible absorption spectra measurement (UV-vis) were used to track the process of photolysis. A systematic study on the effects of pH, molecular weights, and secondary structure on the self-assembly of diblock copolymers was performed. We demonstrate that the secondary conformation transition with pH variation dominates the sphere-to-cylinder transition. Remarkably, the hierarchical nanostructures with various dimensions can be obtained from preassembled units with the addition of metal ions.