Oral submucous fibrosis (OSF) is a potentially malignant disorder characterized by the accumulation of extracellular matrix in the oral mucosa, which leads to stiffening and can potentially result in trismus. There is still a lack of effective measures to prevent and treat OSF. Nitrate has been verified to provide protective responses against fibrotic diseases in multiple organs and tissues. It remains unclear whether dietary nitrate can prevent OSF. In the present study, we established a OSF rat model to evaluate the effect of nitrate for preventing OSF. Nitrate treatment demonstrated promising preventive effects, including the alleviation of mucosal pallor, improved mouth opening, and ameliorated histopathologic features in rats with OSF, with no side effects. Moreover, nitrate also inhibit collagen deposition, profibrogenic marker expression, and inflammation. RNA-seq analysis of fibrotic oral mucosal tissues, followed by functional verification, revealed that nitrate’s preventive effect is primarily mediated through inhibition of the PI3K/AKT signaling pathway, ultimately leading to reduced expression of fibrosis-related markers. Our findings revealed for the first time that nitrate exhibited strong preventive effects in both in vitro and in vivo models of OSF by inhibiting the PI3K/AKT signaling pathway. Dietary nitrate supplementation could offer a novel, safe, and effective approach to preventing OSF.