This study was performed to investigate sequential vascular dynamics during bone regeneration by electrical stimulation.<BR>Osseous defects (∅ 1.8 mm) were created in adult male Wistar rat femur. Osseous defects of groups A and B were covered with nonpoling or poling VDF/TrFE film, and osseous defects that received no film served as the control group. After 3, 5, 7, and 14 days, the vascularization was evaluated by SEM of the vascular corrosion cast and LM of transparent preparations by India ink injection. The results were as follows:<BR>Osseous defects of the control group were supplied with elongation and anastomosis of newly-formed vasculature which derived from periosteum and bone marrow. Newly-formed vasculature in osseous defects of groups A and B derived from bone marrow. In group B, the diameter and density of newly-formed vasculature increased in each experimental period, although the vascularization was delayed in group A. A newly-formed vasculature elongated to osseous defect with a small angle of branches.<BR>It was concluded that electrical stimulation activated the vascularization and provided the change of the vascular architecture that influenced the direction of bone formation within the experimental period.