High-entropy oxides (HEOs) have attracted significant attention owing to their broad compositional tunability and high catalytic activity. However, research in this area is still in its early stages, and it is necessary to develop uniform multifunctional high-entropy nanozymes with appropriate sizes and excellent catalytic properties. In this study, we synthesized spherical high-entropy oxide composite carbon (HEO/C) nanoparticles (NPs) with a uniform distribution of particle size. The HEO/C NPs showed efficient peroxidase and catalase activities and photothermal conversion properties in the near-infrared (NIR) biological window. Compared to conventional Fe