Cerium oxide-based nanozymes have recently drawn much attention in the field of biomedical and antioxidant applications, because of their unique regenerative or autocatalytic properties. Herein, we studied the biomimetic superoxide dismutase (SOD) nanozymes CeO2-Gd that combines the fluores-cence properties of rare earth Gd with the antioxidant properties of CeO2 nanoparticles, which was prepared via facile route. The structure and composition of the CeO2-Gd were measured and verified by X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray electron spectroscopy (XPS). Confocal microscopy was used to image cells. Antioxidant performance and cell viability of these nanozymes were measured in vitro using BGC-803 cell. CeO2-Gd nanozymes with a higher Ce3+/Ce4+ratio show higher superoxide dismutase (SOD) mimetic activity. Their antioxidant activity and fluorescence properties of CeO2-Gd in BGC-803 cancer cells are enhanced by oxygen vacancies generated by doping rare-earth elements Gd. This work may guide the future design of CeO2-Gd-based biomimetic nanozymes for anticancer and antioxidant applications.