Oxidative stress is occurred under excessive reactive oxygen species (ROS) production and/or imbalanced cellular anti-oxidant defense system, which is widely recognized as a key factor in developing liver diseases. Therefore, agents ameliorating oxidative stress may bring great benefit to prevent and/or treat liver diseases. To identify novel hepatoprotective agents, two herbal medicines, Penthorum chinense Pursh (P. chinense) and Garcinia mangostana L. (G. mangostana) were chemically investigated under the guide of tert-butyl hydroperoxide (t-BHP) induced oxidative injury assay in L02 cells. We found that a fraction (E50M60) from water extract of P. chinense was effective in protecting L02 cells from being damaged by oxidants. Further isolation of this fraction resulted in identification of ten flavonoids. Among all the isolates, quercetin showed the most significant protective effect on t-BHP induced hepatocytes damage, which was responsible for the activity of E50M60 fraction. Further study demonstrated that both E50M60 fraction and quercetin attenuated t-BHP induced hepatocytes apoptosis through up-regulation of the expression of B-cell lymphoma 2 (BCL-2) and BCL-xL, and down-regulation the cleaved products caspase-7, -9 and poly (ADP-ribose) polymerase (PARP). Moreover, E50M60 fraction and quercetin up-regulated nuclear factor erythroid 2-related factor 2 (NRF2) and heme oxygenase-1 (HO-1) expressions and down-regulated Keap-1 expression, which resulted in resistance to the ROS induced mitochondrial oxidative stress. Meanwhile, we found that γ-mangostin (γ-man) isolated from G. mangostana significantly increased the cell viability challenged with t-BHP with low toxicity compared with other xanthones. γ-Man significantly ameliorated t-BHP induced ROS iv accumulation, mitochondrial membrane depolarization and nuclei morphology change in L02 cells. t-BHP decreased intracellular key enzymes and lipid peroxidation, increased the levels of superoxide dismutase, and reduced glutathione; while, treatment of γ-man almost reversed these changes. Further experiments were performed to explore the potential mechanisms for the hepatoprotective effect of γ-man. The results showed γ-man stimulated the nuclear translocation of NRF2 to enhance antioxidant capacity, which was partially reversed by treatment of the NRF2 inhibitor, all-trans-retinoic acid. Moreover, γ-man increased the expression and activity of silent mating type information regulation 2 homolog 1 (SIRT1), which facilitated the deacetylation of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) to improve the mitochondrial function in L02 cells. The protective effect of γ-man was partially blocked by treatment of the SIRT1 inhibitor tenovin-1 or SIRT1 knockdown. In vivo studies showed γ-man protected mice from carbon tetrachloride-induced acute liver injury in mice, through up-regulation of NRF2 and SIRT1 to enhance protective capacity. Subsequently, the improvement of liver fibrosis by γ-man was investigated in human immortalized hepatic stellate cells (LX-2) and carbon tetrachloride (CCl4) chronic injured mice. The results indicated that γ-man significantly decreased the expression of collagen I and α-smooth muscle actin (α-SMA) in LX-2 cells in both dose and time dependent manner. Mechanisms studies found that the anti-fibrotic effect of γ-man was related to induction of sirtuin 3 (SIRT 3) in LX-2 cells, which facilitated the inhibition of NADPH oxidase (NOX) and activation of histone deacetylase (HDAC1) to increase the deacetylation of high mobility group box 1 (HMGB1) protein. The increased deacetylated HMGB1 by treatment of γ-man impaired HMGB1 shuttling from nuclei to cytoplasm, which decreased the autocrine v stimulation effect in LX-2 cells. Meanwhile, it was found that γ-man attenuated the activation of LX-2 cells by auto-secreted HMGB1 through PI3K/AKT and MAPK p38 pathways. Then, the anti-fibrotic effect of γ-man was evaluated in vivo. The results indicated that γ-man showed significant protective effect in CCl4 induced chronic liver injury in mice. Related protein analysis demonstrated that treatment with γ-man significantly increased the expression of SIRT3, which was accompanied by the decreased expression of collagen I and α-SMA in mice liver. Consequently, γ-man might be a candidate to improve chronic liver injury through induction of SIRT3 and interference of HMGB1 signaling axis. Collectively, our findings indicate that both P. chinense and γ-man might be potential candidates for treatment and/or prevention of liver diseases, which are deserved for further development.