Objective: Bone marrow-derived mesenchymal stem cells (BM-MSCs) are multipotential cells. However, the harvest of autologous MSCs can be difficult due to the age or poor physical status of patients. The aim of this study was to investigate the reconstructive effect of allogeneic BM-MSCs on segmental mandibular defects. Study Design: Freeze-dried and perforated mandibles of beagles were prepared as scaffolds. The right mandibular body of 24 female beagles was cut into 30 mm to create a segmental defect. The defects were randomly repaired with allogeneic freeze-dried bone (group A) or allogeneic MSCs and freeze-dried bone (group B). The reconstructive effects on the 2 groups were assessed by conducting computerized tomography scanning and histological analyses. Results: The continuity and integrity of both groups were restored. The osseous maturation of group B was higher than that of group A. Conclusion: Allogeneic MSCs can promote new bone formation and improve the reconstructive effect on segmental defects. © Science Printers and Publishers, Inc.