UNLABELLED: Ternary copper-based chalcogenide nanomaterials have become rather attractive due to the near-infrared (NIR) response in cancer theranostic fields. However, it is still challenging to further improve the theranostic efficiency of these nanomaterials. Herein, Cu-Sb-S nanoparticles (NPs) around 24 nm are synthesized facilely and functionalized with poly(vinylpyrrolidone) (PVP). Under the NIR irradiation, the resultant PVP-Cu-Sb-S NPs exhibit a relatively high photothermal conversion efficiency of 53.16% and a simultaneous reactive oxygen species (ROS) generation effect. Due to these outstanding photothermal/photodynamic effects, excellent tumor ablation results can be achieved by the combination of PVP-Cu-Sb-S NPs and 808 nm NIR laser treatments without obvious side effect. In addition, they show remarkable contrast enhancement according to in vitro and in vivo photoacoustic (PA) imaging. These PVP-Cu-Sb-S NPs could be served as a multifunctional nanotheranostic agent for PA imaging, photothermal/photodynamic cancer therapy. STATEMENT OF SIGNIFICANCE: Highly theranostic efficiency ternary copper-based chalcogenide nanomaterials has not been fully developed yet. Herein we report the PVP-Cu-Sb-S nanoparticles (NPs) with relatively high photothermal efficiency, simultaneous reactive oxygen species generation effect and photoacoustic imaging capability. The photothermal conversion efficiency of PVP-Cu-Sb-S NPs is higher than most of copper-based chalcogenide nanomaterials reported before. These findings provide a new kind of ternary copper-based chalcogenide with an enhanced theranostic effect, which could be served as a promising multifunctional nanotheranostic agent in the field of biomedical application.