Objective:To study the role of G-protein coupled receptor kinase-interacting protein 1 (GIT1) in fracture healing. Methods: GIT1 knockout(KO) mice (n=30) and GIT1 wildtype(WT) mice (n=30) were used to established the femoral model according to our pervious study. Immunohistochemical (IHC) staining was used to detect the endochondral mineralization and the expression of Smad1/5/8 in callus area. Bone marrow mesenchymal stem cells (BMSCs) of GIT1 WT and KO mice were collected and stimulated with 10 ng/mL BMP2,and then the expression of p-Smad1/5/8 and the level of p-Smad1/5/8 translocated into the nuclei of BMSCs were detected. One μg of GIT1-siRNA (or control-siRNA) was co-transfected into C3H10T1/2 cells. Luciferase reporter genes was used to detecte the influence of GIT1 on BMP2 transcription. Results:GIT1 KO mice exhibited delayed fracture healing,chondrocyte accumulation in the fracture area,and reduced staining intensity of phosphorylated Smad1/5/8 (p-Smad1/5/8). BMSCs extracted from GIT1 KO mice showed a decline of p-Smad1/5/8 levels and of p-Smad1/5/8 translocated into the cell nucleus after BMP2 stimulus. The results of luciferase reporter gene assay showed that the level of intracellular GIT1 protein significantly affected the level of BMP2 transcription through p-Smad1/5/8. Conclusion: GIT1 regulates Smad1/5/8 phosphorylation and mediates BMP2 regulation,thus affecting endochondral ossification.