Many different appliances have been used to move teeth or to attempt to inhibit or stimulate growth of the jaws. Especially. Orthopedic force was used to apply a constant force on the mandible. Various orthopedic forces bring the changes of surrounding tissue, growth and development on the mandibular joint Authoe carried out this study to find the histological changes of. the mandibular joint in rats when the mandible applied posterior displacement. For the purpose of this study, 009- x 036inch closed coil spring and 030inch orthopedic wire were used between the post occipital region and the chin region in order to render the orthopedic forces, posteriorly. The experimental animals were used 1 month old (Groupl), 3 months old (Group. II), and 12 months old (Group III) rats. Following results were obtained; 1. At the beginning of the experimental Group I, there were predominant increment of Cartilage layer in the posterior parts of condylar head. Especially, the mature chondrocyte zone was increased. 2. In the experimental Group II, the chondroblastic zone was decreased while it showed slightly increased mature cartilage zone. 3. In the experimental Group III, the mature chondrocyte zone was disappeared gradually and there was a tendency to reduce the endochondral bone formation in condylar head. 4. After 30 days of experimental Group I and in experimental Group II, there was a tendency to decrease the immature cellular zone in the glenoid fossa by pressure. 5. There were no histological changes in the articular disc by pressure.