Introduction: In various studies, administration of Biochanin A (BCA), aneuroprotective, anticancer, anti-oxidant, anti-inflammatory, anti-allergic, anti-hyperglycemic and anti-hyperlipidemic effects significantly decrease the injury in the brain associated with cell death and enhanced neurotransmitter release and activity. Biochanin A, the predominant phytoestrogens in the plant, mainly include isoflavones. Reports about the effect of phytoestrogens on the central nervous system, especially behavioral assessments, have been controversial. Thus, the aim of this study was to determine the neuroprotective and behavioral effects of Biochanin A in the acute phase following diffuse traumatic brain injury (DTBI) in male rats. Material & method: Male rats were given either Biochanin A or an equal volume of vehicle (DMSO; 50 mg/kg) at 1h after DTBI. Non-injured controls (three groups: with dimethyl sulfoxide (DMSO), and Biochanin A and one group that was untreated (sham group) and DTBI (with DTBI and without treatment) animals were also included. The animals at 24h post trauma were evaluated daily over 12 days for motor and cognitive outcomes. After two weeks, the animals were perfused with 0.9% saline followed by 10% phosphate-buffered formalin. The whole brain was dissected and removed, sliced, and stained with Cresyl Fast Violet (dark cell) and immunohistochemistry (GFAP and caspase-3 positive cells). Result: Biochanin A decreased dark cell numbers (P<0.01) and reduced cerebral cortical levels of GFAP and caspase-3 positive staining (respectively, P<0.0001 and P<0.0001). The researchers investigated the levels of brain edema in the injured animals and found that Biochanin A significantly increased the wet weight/dry weight ratios after brain injury (P<0.01). This increase was associated with an increase in permeability of the blood–brain barrier and was present up to 4 h post-injury, assessed using Evans blue dye (P<0.01). Conclusion: Biochanin A given acutely after injury decreased apoptotic-mediated cell death, dark cells and secondary injury with reduced astrogliosis. These results suggested that phytoestrogens such as Biochanin A might afford protection to those suffering from DTBI.