<p>Traumatic brain injury (TBI) is a severe form of cranial trauma that is associated with high disability and mortality rates, imposing substantial physical, psychological, and economic burdens on affected individuals. Formononetin (FN), a well-characterized phytoestrogen, exhibits diverse biological activities, most notably anti-inflammatory and antioxidant effects, and has demonstrated neuroprotective potential in TBI scenarios. Previous <b>s</b>tudies have shown that FN is capable of upregulating the expression of microRNA-155 (miR-155), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) in TBI rat models. However, the precise function of miR-155 and its interaction with the Nrf2/HO-1 pathway remain incompletely elucidated. Herein, we investigated the therapeutic impact of FN on TBI pathophysiology and its underlying neuroprotective mechanisms, with a specific focus on miR-155 inhibition. Our findings showed that FN treatment notably improved neurological function, reduced cerebral edema, attenuated histopathological damage at the site of injury, decreased neuronal apoptosis, enhanced the performance in the Morris water maze, decreased inflammatory cytokine levels, and upregulated the expression of miR-155, Nrf2, and HO-1 in TBI rats. These observations suggest that FN has neuroprotective effects in TBI. Notably, when miR-155 was inhibited, the neuroprotective effects of FN were partially abrogated, accompanied by downregulated Nrf2 and HO-1 expression. This suggests that the protective effects of FN are likely mediated by miR-155-dependent modulation of the Nrf2/HO-1 pathway, providing valuable insights into the potential therapeutic use of FN and its derivatives for TBI management.</p>