Objective：To study the changing rules of glial fibrillary acidic protein（GFAP） expressions in the rat brain after traumatic brain injury（TBI） and to observe the effect of Simvastatin（SIM）on them based on the TBI rat model. Methods：Totally 54 Sprague-Dwalye（SD） rats aged 5 weeks were employed and divided into sham TBI group，control group and treatment group（n=18）. TBI model was established in control group and treatment group by Feeney’s method. The rats in treatment group were fed SIM 10 mg/kg in the evening pre-injury and in every evening post-injury while those in control group were fed the same dose of starch each time. Then the rats were sacrificed and the rat brains were collected at different time points（3，12，24 h and 3，7，14 d post the injury）. The changes of GFAP expressions in cornu ammonis（CA） area were detected with immunohistochemistry. Results：The GFAP positive cell percentage was higher in control group than in sham TBI group at 3 h after the injury. The GFAP positive cell percentage reached the peak at 3 d and 7 d after the injury（P＜0.01）. The positive expression of GFAP was significantly lowered in treatment group than in control group at 7 d after the treatment（P＜0.05）. There was no difference at 1，2，3 d and 14 d after the treatment between con－trol group and treatment group（P >0.05）. Conclusion：SIM treatment could decrease the over-expression of GFAP in rats after TBI.