Shanxi aged vinegar (SAV), a kind of typical fermented food, is one of the famous traditional vinegars in China. In this study, the antioxidant properties and hepatoprotective mechanisms of SAV on hydrogen peroxide (H₂O₂)-induced oxidative stress were investigated. Total phenolic, flavonoid contents and browning index were increased during the aging process. Gallic acid was the main component of the phenolic compounds in SAV-5. SAV-5 showed the highest antioxidant activities among all the samples. In addition, H₂O₂ was used to treat human normal hepatocyte LO2 as an inducer of oxidative stress models. Pretreatment with SAV-5 inhibited H₂O₂-induced cytotoxicity and reactive oxygen species (ROS) generation, and alleviated loss of mitochondrial membrane potential in LO2 cells. These pretreatments also significantly increased superoxide dismutase (SOD), catalase (CAT) activities and glutathione (GSH) levels. The results demonstrated that SAV-5 had a significant antioxidant effect, which could prevent oxidative damage in LO2 cells effectively. Finally, SAV-5 activated nuclear factor erythroid-2-related factor 2 (Nrf2) and up-regulated NAD(P)H quinone oxidoreductase 1 (NQO1) and heme oxygenase (HO-1) protein expression in H₂O₂-treated LO2 cells. The protective effects of SAV against H₂O₂-induced oxidative damage in LO2 cells are mainly mediated by the activation of the Nrf2 antioxidant pathway. This study explored the fermented food products with antioxidant activities and the possible hepatoprotective mechanism of traditional Chinese vinegar against oxidative damage in liver cells.