Sleep apnea syndrome(SAS)was revealed to be a modern disease because of the skeletal morphology, lifestyle habit and mental stress of modern humans. Approximately 400 thousand SAS patients have been diagnosed and treated in Japan and numbers of potential SAS patients were estimated at more than 5 millions. Contemporary therapy for SAS is continuous positive airway pressure(CPAP)therapy in medical for moderate or severe SAS and oral appliance(OA)therapy in dental for mild SAS patients. However recent study shows OA therapy is effective even for moderate or severe SAS. In this review, outlines and current status of OA therapy will be discussed.