Objective To investigate the expression of Toll like receptor 4(TLR4)in the injured brain tissue atter traumatic brain injury(TBI) and explore the potential role of TLR4/NF-κB in the secondary brain injury.Methods Thirty-six SD rats were randomly divided into control group(n=1 2),TBI inducement for 1 d group(n=6),TBI inducement for 3 d group(n=12)and TBI inducement for 7 d group(n=6).TBI models of the later 3 groups were induced by Feendy's free-falling,and rats of the control group are only performed exposure ofdura of the right parietal lobe.TLR4 mRNA expression in the injured brain tissue was studied by RT-PCR,NF-κB binding activity was detected by electrophoretic mobility shift assay (EMSA),and the TNF-α and IL-6 levels were detected by enzyme linked immunosorbent assay(ELISA).Immunohistochemistry was employed to determine the protein expression of TLR4 in the brain tissues of control group and TBI inducement for 3 d group.Results The TLR4 mRNA expression,NF-κB binding activity,and the levels of TNF-t and IL-6 in rats of the TBI inducement for 1,3 and 7 d groups were significantly increased as compared with those in the control group(P＜0.05).The protein expression level of TLR4 in the brain tissue of control group was rare,and a large number of TLR4-positive immunostained cells,including cortical glial cells and neurons,were noted in the brain tissue of TBI inducement for 3 d group.TLR4 mRNA level was positively correlated to the NF-κB activity(r=0.786,P=0.000),and positive relations were also noted between TLR4 mRNAlevel and both TNF-α and IL-6 levels(r=0.517,P=0.010; r=0.503,P-0.012).Conclusion TBI could induce concomitant and persistent up-regulation of TLR4 expression and NF-κB binding activity in the injured brain tissue.TLR4/NF-κB might play a central role in the secondary injury after TBl.