Cs0.33WO3 nanoparticles show excellent near-infrared photothermal conversion property. Plasmonic nanomaterials could exhibit special absorption via the excitation of surface plasmon, and the maximum absorption band was highly sensitive to the particle’s size, shape, local environment, and the coupling between near nanoparticles. Furthermore, under optical illumination, they could convert the absorbed photon energy into heat energy in approximately 1 ps and then transfer the heat to the surrounding media in tens of picoseconds. Such an efficient light-to-heat conversion property made them become useful as nanoheaters and therefore gain more and more attention in the past decade. The NIR photothermal conversion property of the resulting Cs0.33WO3 powder after grinding for various times was studied to demonstrate the excellent NIR photothermal conversion property of Cs0.33WO3 nanoparticles.