Sleep apnea syndrome is very common breathing disorder, which can cause significant health problem and poor quality of life. Among several treatments of sleep apnea syndrome, oral appliance treatment has been used effectively in some sleep apnea syndrome. Since then, mandibular advancement devices (MAD) have become a common treatment for obstructive sleep apnea (OSA) and are used to increase the caliber of the airway during sleep. Nevertheless, it appears that only a small percentage of patients will quit using a MAD because of temporomandibular joint (TMJ) or masticatory muscle soreness. So patients using MADs must be monitored regularly for ongoing efficacy and for associated complications. In this article, the history of MAD and the efficacy of this appliance for OSA will be discussed.