Poly( N-isopropylacrylamide)/chitosan (PNIPAM/CS) core–shell microgel was synthesized by graft copolymerization. The microstructure of copolymers was characterized by FT-IR spectrum and 1H-nuclear magnetic resonance ( 1H NMR). Transmission electron microscope (TEM) and dynamic light scattering (DLS) measurements display that the microgel has high monodispersity and with a core–shell structure. For swelling the microgel in various alcohol solutions, the particles first shrink; then flocculation occurs resulted from weak aggregation of particles with the increase of alcohol concentration. The investigation of the size of microgels as a function of temperature shows that the thermo-sensitive property is markedly exhibited when the alcohol concentration is low, and vanishes when the alcohol concentration exceeds some value where the microgels have the lowest size.