Objects: To test the hypothesis whether bone marrow stem cells (BMSCs) could migrate into the periodontium as the precursor available for the repair of tissue injury. Methods: A chimeric mouse model was established by transplanting BMSCs derived from red fluorescent protein mouse into irradiated BALB/c mice. Subsequently, a periodontal defect was created beside the maxillary first molar and filled with ceramic bovine bone. Finally, the chimeric mice were divided into three groups and were observed 3, 14 and 28 days later respectively. The involvement of BMSCs in periodontal defects was analysed using an in vivo imaging system and immunohistochemical staining of CD45, CD105 and CD31. Cell surface marker expression in injured tissue was also compared with that in normal tissue. Results: Increasing numbers of BMSCs migrated into the periodontal defect with time. The distribution was initially limited to ceramic bovine bone and then around blood vessels and near alveolar bone. Furthermore, expression of CD105 and CD31 was much higher in injured periodontal tissue than that in healthy periodontium, although CD45 was not expressed in either of these tissues. Conclusion: BMSCs, but not haemopoietic stem cells, were involved in periodontal defect; they entered the periodontium probably via blood vessels. Keywords: bone marrow stem cell (BMSC), red fluorescent protein (RFP), periodontal ligament stem cell (PDLSC)