The changes of the dental arch form after the tooth movement and the sequential changes occurred on the palate during orthodontic treatment were examined in the coordinate system based on the standard point at the palatal vault. The subjects selected for this study were 20 patients of Angle Class II div. 1. Both left and right maxillary premolars were extracted and an edgewise appliance had been treated. The plaster models prepared before and after treatment were used for materials. Only suitable materials were measured as a result of an examination of the reproducibility of the palatal core at the palatal vault. Results obtained were as follows: 1. It was suggested that the dental arch and the palate was mutually effected on each other in the arch length and the arch width. 2. The morphological changes in the dental arch and the palate due to orthodontic treatment was discussed on the basis of the results of Fourier analysis. The dental arch and the area from F division to J division were significantly smaller after orthodontic treatment than before it. The shape became closer to a semicircle. 3. Values representing morphological changes in the dental arch and J division were similar and values representing morphological changes in the other division were getting smaller as the area being close to the palatal vault.