Rett syndrome is progressive neurodegenerative disorder in female patients, characterized by autistic behavior, mental retardation, loss of purposeful hand skills, stereotypic hand movement, breathing dysfunction, severely impaired language, ataxia, and seizure. The diagnosis of Rett syndrome is based on its characteristic clinical manifestation and course. The electroencephalographic (EEG) findings of Rett syndrome are nonspecific, but a progressive deterioration in the EEG, characterized by a slowing of background activity and spike sharp wave discharges, may be observed. We experienced one case of Rett syndrome in a 5 year old girl having mental retardation, loss of purposeful hand skills, stereotypic hand movements (clapping, washing, hand-to-mouth), breathing dysfunction (hyperventilation/apnea). Her EEG findings on Video-EEG monitoring are excessive slowing waves during awake state and frequent spike discharges from left or centrotemporal area during sleeping. We report a case of Rett syndrome with brief review of related literatures.