Obstructive sleep apnea syndrome(OSAS) is a common chronic disorder in children and adolescents, dramatically affecting systemic health and development. A small maxilla may cause sleep-disordered breathing in children. Rapid maxillary expansion(RME) is widely used by orthodontists to increase the maxillary transverse dimensions of young patients. Recent studies suggested that RME can effectively manage pediatric snoring and significantly improve OSAS. This study aims to investigate the efficacy of orthopedic RME in treating pediatric OSAS.