The purpose of this study was to evaluate the bone-forming capacity of the periosteum in calvaria of rats. The experiment was carried out in 49 rats. We exposed the calvaria and made 1㎝ diameter round full thickness defect at both sides of calvaria. In the left calvarial bone serving as control, the periosteum was removed after implantation of block, while in the right calvarial bone the periosteum remained intact as an experimental site. The histologic examination of bone response was performed after 1-, 2-, 4-, 6-,8-, 12-, 24-week implantation in calvaria of rats. We could observe the periosteal preservation favorably influenced the bone formation.