Objective To evaluate the dynamic changes ofmiRNA-21 expression in injured brain tissues of rats with traumatic brain injury (TBI),and explore the effect of ectogenic miRNA-21 on neuronal apoptosis of the rats and their neurological functions.Methods Eighty-four rats were randomly divided into sham-operated group,TBI model group,blank-intervention group and miRNA-21-intervention group (n=21).Rats in the sham-operated group were only performed scalp incision and window bone removal without beating,and those in the other three groups were performed beating to induce TBI models; liposomes with/without miRNA-21 were injected into the latter two groups.Several time points after the brain injury/intervention:12,24,48 and 72 h,and 1 and 2 weeks,respectively,were chosen to measure the neurological functions using Modified Neurological Severity Scale (mNSS) and footfault test.Then,the animals were sacrificed to observe the miRNA-21 expression levels by using quantitative real-time-PCR and to examine the neuronal apoptosis in rat cerebral corticesby TUNEL.Results The miRNA-21 expression began to obviously increase in injured brain tissues at 2 h after TBI,peaked at 48 h after TBI in the cerebral cortices; the miRNA-21 expression level was still higher than that in the sham-operated group 7 d after TBI (P＜0.05); the miRNA-21 expression level was higher than that in the TBI model group and blank-intervention group at 24,48 and 72 h after TBI (P＜0.05).Began with 24 h of TBI,mNSS showed that the scores of miRNA-21-intervenion group were significantly lower than those in the TBI model group and blank-intervention (P＜0.05).TUNEL indicated that the count of apoptotic cells in the traumatic area of miRNA-21-intervenion group was significantly smaller than that in the TBI model group (P＜0.05) Conclusion MiRNA-21 may be involved in the process of recovery after traumatic brain injury to inhibit the apoptosis in the traumatic area.