Objective To investigate the protective effect of umbilical cord mesenchymal stem cells (UCMSCs) on traumatic brain injury (TBI) in rats.Methods Thirty healthy Sprague-Dawley rats (10 rats for each group) were randomly divided into normal control group (normal),model group (injection of saline after TBI) and UCMSCs transplantation group (injection of UCMSCs after TBI).The rats in experimental groups were sacrificed on the 10th day after UCMSCs transplantation.The percentage of UCMSCs in brain tissue was detected by flow cytometry.The pathological changes of brain tissue were observed by hematoxylin-eosin (HE) staining method.The expressions of vascular endothelial growth factor (VEGF),glial fibrillary acidic protein (GFAP) and brain-derived neurotrophic factor (BDNF) in brain tissue were measured by immunohistochemistry and immunofluorescence double staining.The neurological deficit was evaluated by neurological deficit degree.Results The percentage of CD90,CD73 and CD105 cells in the UCMSCs transplantation group was significandtly higher than that in the model group (0.4％ vs 0.1％,P＜0.05).The results of HE staining showed that the brain injury of the transplanted group was alleviated compared with the model group (P＜0.05).The VEGF of the brain tissue in injury area in the UCMSCs transplantation group was higher than that in the model group (P＜0.05).The number of GFAP and BDNF positive cells in the UCMSCs transplantation group was higher than that in the model group (P＜0.05),and the neurological deficit score was also higher than that in the model group (P＜0.05).Conclusions UCMSCs transplantation for the treatment of TBI rats can effectively reduce the vascular damage in the injury area and promote nerve recovery.