The purpose of this study was to evaluate the effect of splinting methods on the rearrangement of periodontal fibers after experimental tooth movement. Orthodontic force was applied by placing closed coil spring between upper third incisor and canine in seven dogs, weighing 20kg or more. After 3 weeks of force application, 0.025 inch multistrand wire and polyethylene ribbon were bomded to each side, as a flexible and rigid splinting respectively in 6 experimental animals. The remaining one served as a control. Each two animals were sacificed at 4, 8 and 12 weeks after splinting respevticvely and prepared histologically for hematoxylin-eosin and Masson´s trichrome staining. The results of this study were odtained follows: 1. After tooth mocement, periodontal space was narrowed and periodontal fibers were thick on pressure side while elongated fibers were observed on tension side. 2. After 4 weeks of retention, the rearrangement of periodontal fibers was observed in the flexible splinting group, but not in the rigrd splinting group. 3. After 8 weeks of retention, the rearrangement of periodontal fivers was obwerved in both groups, but the difference could not be detected between two groups. 4. During the retention period, the rearrangement of periodintal fibers was faster in tension side than in pressure side. There results show that the rearrangement of periodontal fibers is also obtained by rigid splinting after tooth movement. It is suggested that the rigid splinting by polyethylene ribbon can be used as way of postorthodontic retention.