Purpose: The effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and osteogenically differentiated adipose tissue-derived stem cells (ADSC) on new bone formation in high-speed distraction osteogenesis of adult rabbit cranium were investigated. Materials and Methods: A total of 41 adult rabbits were used in the study. Distraction began after a 5-day latency period at a rate of 1.5 mm twice a day until 10-mm length gain was obtained both in the control group, where a bone defect was induced, and in the experimental group, in which ADSC (group A), rhBMP-2 (group B), or both (group C) were injected in the distraction gap after distraction. At 4, 8, and 12 weeks after distraction, computed tomography analysis was done to determine the bone defect dimension and bone mineral density (BMD), while histologic examination was also done to calculate bone formation ratio. Results: Bone defect dimension significantly decreased in groups B and C, compared with the control group, at 4 and 12 weeks after distraction. BMD was significantly increased in groups B and C at 4 weeks. On histologic examination, bone formation ratio was significantly increased in group C only at 12 weeks. Conclusion: This study suggests that the use of rhBMP-2 in combination with or without ADSC is helpful to promote bone regeneration in high-speed distraction osteogenesis of adult rabbit cranium.