Artificial nanoenzymes with enzyme-like catalytic activity have gradually become substitutes for natural enzymes due to their low production cost, high stability, and good tolerance. In recent years, with the rapid development of nanotechnology, various enzyme mimics have emerged. With unique properties such as high specific surface area, high porosity, tunable morphology, and excellent biocatalytic properties, nanoenzymes have broad application prospects in the fields of biosensing, biocatalysis, biomedical imaging and therapy. This chapter systematically summarizes the latest research progress of nanoenzymes, including the catalytic principle, classification, and related applications of nanoenzymes, which are classified into two categories: tumor imaging and therapy. Finally, the current challenges and future perspectives of nanoenzymes are also discussed. It is hoped that this review of this important field will provide meaningful guidance for tumor therapy, biosensing, and so on.