Novel photoresponsive nanogels were prepared by the self-assembly of spiropyrane-bearing pullulan (SpP). The solution properties of the nanogels could be controlled by photostimulation via isomerization between hydrophobic spiropyrane and hydrophilic merocyanine. The molecular chaperone-like activity of the nanogels in protein refolding was investigated. The activity of citrate synthase significantly increased when the amphiphilicity of SpP nanogels was switched by photostimulation.