Abstract： Objective To investigate the effect of acute?phase hypothalamic?pituitary?adrenal axis damage and function on neurological function,and learning and memory at the acute phase in rats with severe traumatic brain injury(TBI). Methods Sixty healthy male adult SD rats were randomly divided into sham operation group, model group and Dexamethasone group (n=20 each). The model group and Dexamethasone group were treated with Feeney method,and the rat TBI models were established. The Dexamethasone group was injected with 0.6 mg/kg Dexamethasone intraperitoneally at 10 min,24,48 and 72 hours after injury. The other two groups were treated with equal volume of normal saline. The changes on the levels of peripheral blood corticosterone,adrenocorticotropic hormone(ACTH)and neuronal apoptosis at 3,12,24 and 72 hours after the injury were measured and compared among the three groups. The differences in the neurological scores at 1 and 7 d after the injury,and the findings of the water maze test at 7 days after the injury were determined. Results The levels of peripheral blood corticosterone,ACTH,water maze latency,and neuronal apoptosis at the different time points after the injury in the model group and Dexamethasone group were significantly increased (P<0.05). The levels of peripheral blood corticosterone and ACTH after the injury in the Dexamethasone group were significantly higher than those in the model group(P<0.05),whereas the water maze latency and neuronal apoptosis were significantly lower than those&nbsp;in the model group(P<0.05). The percentage of water maze quadrant at different time points after the injury in the model group and Dexamethasone group was significantly lower than that in the sham operation group (P<0.05),whereas the percentage of water maze quadrant after the injury in the Dexamethasone group was significantly higher than that in the model group (P<0.05). Conclusion Changes in the hypothalamic?pituitary?adrenal axis function at the acute phase in rats with TBI are found that the levels of corticosterone and ACTH are increased. It may be related to the damage of neurological function,and learning and memory.