Cellulose nanocrystal (CNC) prepared by hydrolysis of cotton linters with sulfuric acid was used to react with chloroauric acid to manufacture a gold nanoparticle/CNC composite. The composite was then graft-copolymerized with N-isopropylacrylamide to obtain a photo-thermal ultrafine gold nanoparticles/CNC-based hydrogel. The hydrogel was studied by performing scanning electron microscopy, and it was found that the prepared hydrogel had a network structure. The temperature of the hydrogel increased from 25℃ to 39℃ and its volume decreased by 30% when it was exposed to visible light (400~750 nm) for 1 h. The experiment results indicated that the prepared photo-thermal CNC-based hydrogel has thermal responsiveness and photo-thermal properties.