This study investigates the enzyme-like activities of biogenic ferritins, which are inorganic minerals found in living organisms. The research reveals that the iron cores of ferritins from prokaryotes exhibit higher superoxide dismutase (SOD)-like activity compared to those from eukaryotes. The differences in catalytic capability are attributed to the iron/phosphate ratio in the iron core, which is influenced by the structure of the ferritin. Phosphate in the iron core switches it from a single crystalline to an amorphous iron phosphate-like structure, affecting its affinity to hydrogen protons and its reaction with superoxide. Overexpression of ferritins with high SOD-like activities in *E. coli* increases resistance to superoxide, while knockout or knock-in of ferritin genes in human cells diminishes free radical tolerance. The study highlights the physiological antioxidant role of these nanozymes and their potential in maintaining homeostasis in living organisms.This study investigates the enzyme-like activities of biogenic ferritins, which are inorganic minerals found in living organisms. The research reveals that the iron cores of ferritins from prokaryotes exhibit higher superoxide dismutase (SOD)-like activity compared to those from eukaryotes. The differences in catalytic capability are attributed to the iron/phosphate ratio in the iron core, which is influenced by the structure of the ferritin. Phosphate in the iron core switches it from a single crystalline to an amorphous iron phosphate-like structure, affecting its affinity to hydrogen protons and its reaction with superoxide. Overexpression of ferritins with high SOD-like activities in *E. coli* increases resistance to superoxide, while knockout or knock-in of ferritin genes in human cells diminishes free radical tolerance. The study highlights the physiological antioxidant role of these nanozymes and their potential in maintaining homeostasis in living organisms.