Trauma from occlusion causes apparent changes in the blood vessels of the periodontal ligament. The initial response is primarily mechanical, due to compression, and secondarily characterized by necrotic changes. Recently, many investigators are concerned with vascular changes in relation to the loss of the alveolar bone. Author observed vascular changes of the periodontium in the experimental trauma from occlusion on rats. The results were observed as follows.: 1) There were no remarkable changes in the gingiva. 2) The blood vessels that normally occupied a position closer to the bone surface showed a displace-ment toward the cemental surface due to trauma from occlusion. 3) There were no appreciable changes of the alveolar bone in the initial period of trauma from occlusion, whereas there was excessive resorption of the alveolar bone in the long range.