Abstract： Objective:To explore the effect of seawater immersion on brain function of rats with traumatic brain injury（TBI）and its possible molecular mechanism.Methods:Eighteen adult healthy male SD rats were randomly divided into sham surgery（sham）group，TBI group，and TBI combined with seawater immersion injury（TSI）group，according to random number table method，with 6 rats in each group. The TBI rat models in the TBI group and the TSI group were established with brain impact device. The rats in the sham group and the TBI group after modeling were placed at room temperature of 26.0 ℃ for 10 hours，while the rats in the TSI group was immersed in seawater at the temperature of（26.0 ± 0.5）℃ for 10 hours. After successful modeling，the brain volumes of the hit site in the TBI group and the TSI group were detected，and the changes of imaging results and brain functions of the rat models were detected through magnetic resonance T2-weighted imaging，the modified neurological severity score（mNSS），open field test，and Morris water maze experiment. The injured cortex of the rats was detected by immunohistochemistry，and the expression levels of ferroptosis marker，i.e.，x-CT and（glutathione peroxidase 4，GPX4），were detected by Western blotting.Results:In the sham group，there was no obvious abnormality observed in the brain tissue structure and morphology. In the TBI group and the TSI group，the rats’ brain showed significant cerebral edema，mNSS increased，and the injured brain volumes of the TSI group rats were significantly higher than those in the TSI group rats on the 7th day（ P<0.01）. The results of the open field test and Morris water maze experiment showed that both the TBI group rats and the TSI group rats displayed a decrease in the percentage of time in the middle region，a decrease in the times of finding a platform，and a decrease of the exploration time in the target quadrant of the platform，when comparing with those of the sham group（ P<0.01 or P<0.001）. The HE staining results showed that both the TBI group and the TSI group rats had tissue fragmentation and significant tissue edema at the junctions between normal and injured tissues，and the TSI group was more severe than the TBI group. The expression levels of x-CT and GPX4 decreased in the TBI group and the TSI group when compared with sham group，and the levels of the markers in the TSI group were more significantly reduced（ P<0.01）. Conclusion:TSI can aggravate brain tissue injury，which may be related to the ferroptosis of brain tissue cells due to seawater immersion．