Objective: The aims of this study are to investigate the working mechanism, the characteristics, the clinical application and the suggested modification of the Quad Helix appliance. Methods: A 7-year-old, female patient with Pierre-Rokin syndrome, who was preformed with palatorrhaphy at 21-month-old treated by using a Quad Helix appliance for one year. Results: After one-year treatment, the wide between the maxillary first molars increased 9.65mm, and the wide between maxillary canines increased 5.20mm. The wide between the mandibular first molars also increased 3.60mm, however the wide between mandibular canines decreased 5.20mm. Conclusion: The Quad-helix appears to be a successful Orthodontic appliance to expand the narrow maxillary or mandibular arches.