Abstract: Objective:In order to test the biological activity of recombinant human bone morphogenetic protein 2 （rhBMP-2）.Methods:Affter injection of rhBMP-2 into the mouse muscles, the differentiation of mesenchymal cells and time-course of bone formation was studied during the ectopic bone formation.Results:The rhBMP-2 expressed by E. coli presented great bone-induction activity. 1 day after implantation of rhBMP-2, the mesenchymal cells from muscular loose connective tissues and blood vessels concentrated in the implantation area. On day 5 typical cartilage tissue and chondrocytes appeared. Calcification emerged on day 7. Infantile hematopoietic cells became visible intramedullaryly on day 14, and a large number of reticular bone trabecula and osseous tissues formation and bone marrow cells emerged from bone trebecula gap by day 21~30. Conclusion:The endochondral ossification was the main pattern of bone formation induced by rhBMP-2. Our results indicate that rhBMP-2 can be replaced in the repair of bone defect and treatment of fracture.