Objectiveto evaluate the changes of maxillary bones and teeth after rapid expansion using rapid palatal expander (RPE). Subjects30 Vietnamese children in their growing ages between 6 and 16, with cervical vertebrae at CS2, CS3, CS4 stage on Cephalometric x-rays, were diagnosed with maxillary constriction according to Yonsei index. The patients were treated with the RPE and evaluated before and a month after the expansion on Cone-beam computed tomography (CBCT). ResultsAfter a month of post-expansion, the maxillary arch width increased by 2.35 ± 1.92 mm with p < 0.05 and when comparing with the mandible, it reached the normal value of Yonsei index (AWU6 – AWL6 was −0,0.33 ± 1.57 mm). The inter-molar width increased by 2.91 ± 0.54 with p < 0.001. No statistically significant difference of the palatal depth was found before and after expansion. ConclusionsRPE increased the maxillary arch and inter-molar widths and resolved the maxillary constriction in growing children on CBCT.