Abstract Purpose To investigate the role of Rosmarinic acid (RA) in the prevention of traumatic brain injury and the immunohistochemical analysis of IBA-1 and GFAP expressions. Methods Healthy male rats were randomly divided into 3 groups consisting of 10 rats. Groups were as follows; control group, traumatic brain injury (TBI) group, and TBI+RA group. After traumatic brain injury, blood samples were taken from the animals and analyzed with various biochemical markers. And then IBA-1 and GFAP expressions were evaluated immunohistochemically. Results Significant results were obtained in all biochemical parameters between groups. Immunohistochemical sections showed IBA-1 not only in microglia and macrophage activity but also in degenerative neurons in blood vessel endothelial cells. However, GFAP reaction and post-traumatic rosmarinic acid administration showed positive expression in astrocytes with regular structure around the blood vessel. Conclusion Rosmarinic acid in blood vessel endothelial cells showed that preserving the integrity of astrocytic structure in the blood brain barrier may be an important antioxidant.