Traumatic brain injury (TBI) refers to external force-induced brain damage, characterized with necrosis and cell loss in cerebral cortex. Interestingly, a plant-extract named formononetin (FN) is found to possess promising pharmacological activities, including cellular neuroprotection. Thus, we propose that FN may exert biological protection against TBI and discuss the underlying mechanism. In the current study, a rat TBI model was established via Feeney's classical method, followed by different concentrations of FN treatment. Nissl-special and DAPI-labeled stains were utilized to assess the proliferation of cortical neurons nearing lesioned tissue. The contents of interleukin-6 (IL6), tumor necrosis factor (TNF-α), and interleukin-10 (IL10) in serum and the cortical neurons were determined by ELISA. Further, intracephalic IL10 expression levels were detected through immunoassay and RT-PCR. Interestingly, the results exhibited within the FN-treated TBI rat model indicated elevated cortical proliferation. The levels of IL10 in serum and the cortical neurons were increased following FN treatments, while TNF-α and IL6 levels in the blood were decreased. In addition, both mRNA and protein expression levels of IL10 in the FN-treated TBI rat model were up-regulated in a dose-dependent manner. Collectively, our present findings indicate that FN provides effective neuroprotection against TBI, likely by activating IL10 expression in cortical neurons nearing lesioned tissue to inhibit neuroinflammatory reaction.