Background: The aim of this research was to investigate whether covering of the distracted cranial bone segment with a polycaprolactone (PCL) membrane (guided bone formation) would accelerate the process of osteogenesis in high-speed distraction of adult rabbit. Methods: Eighteen 24-weeks old, 3.0 to 3.5 kg, male New Zealand rabbits underwent routine gradual cranium distraction (group 1), distraction at high speed without the membrane (group 2), and distraction at high speed with a PCL membrane covering the cranium at the distraction gap (group 3). Five days after the cranial osteotomy, the distraction process was initiated at 3 mm per day (1.5 mm twice a day) in group 2 and group 3, and 1 mm per day (0.5 mm twice a day) in group 1 until 10 mm of length gain was achieved. At the consolidation 4 and 6 weeks, the bone mineral density was analyzed by a computerized tomography imaging protocol. The bone formation ratio of each group was compared with Hematoxylin and Eosin stain. The collagen formation of each group was analyzed by Massons' trichrome staining. Results: Radiographic imaging and quantitative data indicated a significant increase in bone mineral density in group 1 and group 3 compared with group 2. Bone formation ratio in histologic analysis showed an increase in group 1 and group 3. Collagen synthesis in group 2 was significantly increased in distraction gap. In group 3, collagen fibers were significantly decreased underneath the PCL membrane. Conclusions: Polycaprolactone membrane covering the bone distraction gap provides an environment for faster bone formation in high-speed distraction.