The purpose of this study was to detect out the changes occured during orthodontic treatment. The sample was consisted of 77 orthodontic patients. For this study 13 linear lengths and arch area were measured in maxilla, mandible respectively and were analyzed statistically. The results were as follows 1. The sequence of changes in the form and dimensions of dental arches following orthodontic treatment was as follows Class I malocclusion, Class III malocclusion, Class II malocclusion. 2. Changes in the form and dimensions of dental arches were greater in extraction cases than those of non-extraction cases. 3. In comparison with maxilla and mandible on the amount of changes following orthodontic treatment in each malocclusion group, significant differences were greatest in class III malocclusion. 4. In comparison with maxilla and mandible on the amount of changes following orthodontic treatment in extraction and non-extraction cases, significant differences were greater in extraction cases than those of non-extraction cases. 5. The amount of changes during orthodontic treatment in extraction and non-extraction cases in male was not different from female´s.