Klinefelter syndrome is a common sex chromosome disorder characterized by the presence of 1 or more extra X chromosomes, and the most prevalent karyotype is 47,XXY. Epidemiological studies have showed that patients with Klinefelter syndrome had a significantly increased risk of psychosis. We presented a case of a patient with Klinefelter syndrome who was characterized by psychiatric symptoms. The patients had been refractory to clozapine and sodium valproate, but a remarkable improvement occurred after a cycle of 11 sessions of modified electroconvulsive therapy.