ObjectiveTo study the effect of bone mesenchymal stem cells (BMSC) transplantation into traumatic brain injury(TBI) rats by the external carotid artery on neurological function and learning and memory.MethodsTen adult SD rats were randomly divided into TBI group ( n =5 ) and BMSC transplantation group ( n=5).Feeney free falling method was used to establish TBI models.The experimental rats were administrated with BMSC via external carotid artery (ECA),while TBI rats were injected with sterile liquid medium of equal volume via right ECA.Neurological function were evaluated according to the modified neurological severity score (NSS) at 1,3,7,15 days.Morris water maze test was used to observe the animal capabilities of place navigation and space exploration at 15 days,then animals were sacrificed.Survival and migration of implanted BMSC in brains under fluorescence microscope. ResultAfter traumatic brain,varying degrees convulsions,paralysis,loss of balance function in rats were found.Compared with TBI group,BMSC transplantation decreased significantly NSS (P ＜0.01 ).BMSC transplantation significantly decreased on escape latency ( ( 20.48 ± 2.29 ) s ) than the TBI group ( ( 85.93 ± 47.48 ) s) (P ＜ 0.01 ).Moreover,BMSC group in the target quadrant dwell time ( ( 28.62 ± 1.72) ％ )and distance ( (29.05 ± 3.08 )％ ) as well as the number of passing the platform (8.00 ± 2.45 ) were significantly higher than the TBI group ( ( 19.37 ± 2.81 ) ％,(21.78 ± 3.06) ％,(2.00 ± 1.87) respectively,P ＜ 0.01 ).Transplanted BMSC could survive and migrate around injury brain through Hochest mark immunofluorescence.ConclusionBMSC can survive and migrate around injury brain by transplantation of external carotid artery,which results in a significant neurological function improvement and learning and memory increase in rats with traumatic brain injury.