Of the researches on periodontal diseases, the changes occurred in the vasculature of peridontal membrane and the surrounding alveolar bone there-to-fore attracts much attention. In order to induce an experimental occlusal trauma, composite resin was added on the occlusal surfaces of mandibular second and third premolars of dogs to raise the bite for a period of time, followed by injection of methacrylate resin (MERCOX) into inferior alveolar artery and dissolution of soft tissues by protainase and examined under the scanning electron microscope (SEM, JEOL 35 C). The results are as follows: After 14 days, a wide range of avascularized area was observed on resin cast of periodontal membrane. The surface of alveolar bone on which the vasculature disappeared did not show resorption process. However, the surface of alveolar bone next to the periodontal vasculature showed undergoing a direct bone resorption. After 30 days, the vasculature of periodontal membrane underwent a morphological change and turned out to appear as a mesh-like vascular network. Certain avascularized regions was observed over the alveolar bone on margin region and cervical region, and it was circumscribed by a vasculature with glomerule-like loops. This vasculature was suspected originating from underlying alveolar bone marrow and connected with the residual vasculature of periodontal membrane. After 60 days, vasculature of periodontal membrane facing teeth appeared quite resemblance with that of health periodontal membrane. Those next to the alveolar bone, however, showed enlargement. In this period, avascularized area was not observed. After 90 days, the vasculature in periodontal membrane lost its original two-layered arrangement and replaced by the irregular arrayed bundle-like vasculature. Longitudinally arrayed mesh like vasculature was observed in certain region of periodontal vasculature. After 180 days, bundle-like vessels arrayed as an ellipse pattern. Also, resorption process could be observed on the surface of alveolar bone and interradicular septum. Experimental study of occlusal trauma on dentition clearly indicated that teeth were showed a mobility in vertical direction and that the vasculature of periodontal membrane were showed depression and elongation for a period of time. It could not show an apposition where were showed by the experimental depression and elongation, so it was only showed the expansible periodontal membrane space by resorption of alveolar bone.