Ergothioneine (ERGO) is a thiol contained in the food that exhibits an excellent antioxidant effect similar to that of glutathione. Although mammals lack a biosynthetic pathway for ERGO, the carnitine/organic cation transporter OCTN1/SLC22A4, which transports ERGO in vivo, is expressed throughout the body, and ERGO is distributed to various organs after oral intake. ERGO is a stable compound that remains in the body for a long time after ingestion. OCTN1 is also expressed in brain parenchymal cells, including neurons, and ERGO in the blood permeates the blood-brain barrier and is distributed to the brain, exhibiting a neuroprotective effect. Recently, the association between central nervous system (CNS) diseases and ERGO has become a research focus. ERGO concentrations in the blood components are lower in patients with cognitive impairment, Parkinson's disease, and frailty than in healthy subjects. ERGO exerts a protective effect against various neurotoxins and improves the symptoms of cognitive impairment, depression, and epilepsy in animal models. The promotion of neurogenesis and induction of neurotrophic factors, in addition to the antioxidant and anti-inflammatory effects, may be involved in the neuroprotective effect of ERGO. This review shows the association between ERGO and CNS diseases, discusses the possible biomarkers of peripheral ERGO in CNS diseases, and the possible preventive and improvement effects of ERGO on CNS diseases.