This study was undertaken to investigate the three dimensional vascular changes of periodontal ligament following orthodontic tooth movement. Experimental tooth movement was carried out in 96 Sprague-Dawley rats with the weight of 250g. They were divided into four experimental groups (each 24 rats). The left maxillary first molar was moved mesially with 25g force in group I, and with 75g force in group II. Each three animals were sacrificed after 1, 6, 12, 24 hours, and 3, 7, 14, 21 days. In group III, 25g mesial force was applied for 3 days, and in group IV, 75g mesial force was applied for 3 days. Then the appliances were removed, and each three animals were sacrificed after 1, 6, 12, 24 hours, and 3, 7, 14, 21 days from removal of appliance. The contralateral molars were used for control group. Casting media was injected via left ventricle and polymerized in warm water. After corrosion of surrounding soft tissue, three dimensional vascular changes were examined using scanning electron microscopy. The findings of this study were as follows: 1. Pressure side of group I and II showed degenerative vascular changes such as vascular compression, reduction of vasculature, leakage of casting media. But, regenerative changes were dominant after 7 days of tooth movement. Although the degenerative vascular changes were more severe in group II, which was exposed to heavy force, the timing of these changes was not different between two groups. 2. Periodontal vasculature was reestablished by the growth of new capillaries and their differentiation and union from the remaining periodontal vessels and vessels of alveolar bone marrow. Although vascular regeneration was more rapid in group I, which was exposed to light force, the vasculature was not fully normalized in both groups even after 21 days. 3. There was no remarkable changes in tension side of group I and II, but looping of capillary, new capillary growth, dilation of vessels, redirection of vessels in the direction of tensile force were occurred. 4. In pressure side of group III and IV, in which appliance was removed after 3 days of orthodontic force, bone resorption was continued even after removal of appliance. Regeneration of vasculature was initiated after 1-6 hours, and it was more rapid in group III than group IV. In both groups, the vasculature was not fully normalized even after 21 days. 5. After removal of appliance, tension side of group III and IV showed vascular compression and loss of vasculature.