The discovery of the peroxidase-like activity of Fe₃O₄ in 2007 has stimulated the emergence of the new, interdisciplinary research field-nanozymes. Many nanozymes based on metal, metal-oxide, and carbon nanomaterials have been developed, which have applications in the areas of environment, food safety, chemical industry, and biomedicine. Accordingly, progress has also been achieved in the theoretical elucidation of the molecular mechanisms of nanozymes. Here, we will review the basic principles of chemical catalysis. Especially, we will summarize the theoretical results that have been made on the molecular mechanisms of nanozymes consisting of precious metals and carbon materials.