The role of the periosteum on osteointegration of Bio-Oss®(Geistlich, Wolhusen/Switzerland) was studied in rabbit calvarial defect. 12 New Zealand white male rabbits between 2.8 and 4 kg were included in this randomized, blinded, prospective study. Each rabbit was anesthetized with Ketamine HCl(5 mg/kg) and Xylazine HCl(1.5 ml/kg). An incision was made to the bony cranium and the periosteum was reflected. Using a 6-mm trephine bur(3i. USA), four 8-mm defects were created with copious irrigation. The defects were classified into barrier membrane(Tefgen®, Lifecore Biomedical, Inc, U.S.A.) only group as a control, Bio-Oss® with barrier membrane group, Bio-Oss® with periosteum covering group, and Bio-Oss® without periosteum covering group. There were 2 rabbits in each group. The wound was closed with resorbable suture materials. Rabbits were sacrificed using phentobarbital(100 mg/kg) intravenously at 1, 2, and 4 weeks after surgery. The samples were fixed in 4% paraformaldehyde, and decalcified in hydrochloric acid decalcifying solution(Fisher Scientific, Tustin, CA) at 4℃ for 2-4 weeks. It was embedded in paraffin and cut into 6 µm thickness. The sections were stained with H & E and observed by optical microscope.