Objective To observe the survival,conversion and function preservation of mesenchymal stem cells(MSC) after transplantation.Methods MSCs from male Sprague-Dawley(SD) rats were isolated and cultured,then were transplanted to bone defect of female SD rats.Tissues were obtained at defferent periolds.Hybridization in situ was performed on the tissues using Y chromosome specific DNA probe labeled with digoxin to observe the transplanted cells on distribution,quantity and function.Results Allogeneic MSCs could survive and proliferate in the bone defect of recipients and formed bony callus with large quantity and good quality.After 90 days of graft,stem cells still survived and distributed in marrow and newly formed bone tissue.Conclusion After transplantation,allogeneic MSCs have a long-term surviving in marrow and new bone tissue and maintain the characteristic of ossification.