High mobility group box 1 (HMGB1), a late phase cytokine of sepsis, is viewed as a potential target for the treatment of sepsis. The authors considered that 13-methylberberine (13-MB) might reduce circulating HMGB1 levels and increase survival in a mouse model of sepsis by activating AMP-activated protein kinase (AMPK). Western blot analysis and vascular contraction testing were performed using RAW264.7 cells and rat thoracic aorta, respectively. The mechanisms responsible were investigated using various signal inhibitors and small interfering RNA techniques. 13-MB significantly reduced HMGB1 release by LPS-activated RAW264.7 cells, and this was prevented by silencing AMPK or p38, or by pretreating cells with p38 MAPKinase inhibitor, suggesting that the activations of p38 and AMPK were responsible for the observed reduction in HMGB1 release. As was expected, 13-MB increased the phosphorylations of p38 and AMPK. Interestingly, phosphorylations of p38 by 13-MB were inhibited by AMPKsiRNA, indicating that AMPK lies upstream of p38. Furthermore, 13-MB concentration-dependently inhibited IκB phosphorylation in LPS-activated RAW264.7 cells, and in aortic rings, co-treatment with 13-MB and LPS for 8 h, in vitro, significantly restored the isometric contraction induced by phenylephrine. Importantly, 13-MB significantly increased the survival rate of LPS-induced endotoxemic mice. These results suggest 13-MB may be useful for treating diseases in which HMGB1 is viewed as a target.