Objective:To compare the arch expansion effect between the Quad Helix (QH) palatal expansion appliance and the rapid palatal expansion (RPE) appliance. Methods:The sample consisted of 27 cleft lip and palate children who required palatal expansion as part of their orthodontic treatment: 13 were treated with the QH and 14 with the RPE. Dental casts were taken before treatment and at the end of the retention period after expansion. Inter-canine width, inter-molar width, and palatal depth were measured in each cast. In addition, occlusal radiographs were obtained before and 2 weeks after expansion to evaluate sutural separation by the appliances. Results: Posterior crossbites were corrected in all patients following expansion. Both the QH and the RPE groups produced significant increases in inter-canine width (2.11 mm and 3.08 mm, respectively) and maxillary inter-molar width (3.49 mm and 4.80 mm, respectively). Neither the QH nor the RPE group demonstrated a significant change in palatal depth (-0.50 mm and -0.46 mm, respectively). The ratio of skeletal change to total expansion was greater in the RPE group (0.30) than that in the QH group (0.18). Conclusion: It was suggested that both the QH and the RPE appliances were capable of expanding the maxillary dentition and alveolar process, and were equally capable of correcting posterior crossbites. RPE was more effective in the midpalatal suture separation. Keywords: cleft lip and palate, palatal expansion, quad helix, rapid palatal expansion