Objective To investigate the changes in the expression level of PDGF in the bone callus of rats with femoral fracture and brain injury to explore the effect of brain injury on the fracture heal ing and the related mechanism. Methods Sixty-four 12-week-old SD rats weighing (356 ± 25) g were randomly divided into 8 groups with 8 rats in each. The rats in groups A1, B1, C1 and D1 had a femoral fracture and a brain injury for 1, 2, 3 and 4 weeks, respectively; the rats in groups A2, B2, C2 and D2 had a mere fracture without a brain injury for 1, 2, 3 and 4 weeks, respectively. After the CR films were taken, the bone callus was obtained 1, 2, 3 and 4 weeks after operation, respectively. Then, the bone callus and its histology were examined by HE staining, the expressions and changes in the level of PDGF were examined by the immunohistochemical staining, and the level of PDGF mRNA was measured by in situ hybridization. Results The CR films showed that the callus formation in the A1-D1 groups was earl ier and greater than that in the A2-D2 groups at the same time point. The HE staining indicated that more fibroblasts and early-stage chondrocytes were found in group A1; some fibroblasts in the fracture interspace and few early-stage chondrocytes were found in group A2; some newly-formed trabecular bones were found at the end of the fracture in group B1; but no trabecular bone formation was found in group B2; woven bone formation and a few chondrocytes between trabecular bones in the fracture interspace were found in group C1; only a few trabecular bones in the fracture interspace were found in group C2；woven bones turned to lamellar bones in group D1；and more immature trabecular bones in the fracture interspace were found in group D2. The positive expression of PDGF and PDGF mRNA was b in the cytoplasms of fibroblasts, mesenchymal cells, vascular endothel ial cells, early-stage chondrocytes, osteoblasts and osteoclasts. The percentage of the positive cells for PDGF and PDGF mRNA in the callus was significantly higher in groups A1-D1 than in groups A2-D2 at the same time point (P lt; 0.05). Conclusion Brain injury can promote the fracture heal ing process, which is probably related to an increase in the expression level of PDGF after the brain injury.