A new approach towards the design of gold nanoshells on carboxylated polystyrene spheres(GNCPSs) is reported here. Gold nanoshells were self-assembled on the surface ofcarboxylated polystyrene spheres by a seed growth method. Chitosan (CHI) was used as afunctional agent of carboxylated polystyrene spheres for attaching gold seeds. The surfaceplasmon resonance (SPR) peak of GNCPSs can be tuned, greatly redshifted, over a broadspectral range including the near-infrared (NIR) wavelength region, which providesmaximal penetration of light through tissue. Irradiation of GNCPSs at their peakextinction coefficient results in the conversion of light to heat energy that producesa local rise in temperature. Our study revealed that the Lewis lung carcinoma(LLC) in mice treated with GNCPSs exposed to a low dose of NIR light (808 nm,4 W cm−2) induced irreversible tissue damage. The tumor volumes of the treatment group by GNCPSswere significantly lower than those of control groups, with an average inhibition rate over 55%(P<0.005). This study proves that GNCPSs are promising in plasmonic photothermal tumortherapy.