High mobility group box 1 (HMGB1) was recently shown to be an important extracellular mediator of severe vascular inflammatory disease, sepsis. Lysozyme protects us from the ever-present danger of bacterial infection and binds to bacterial lipopolysaccharide (LPS) with a high affinity. Here, we show, for the first time, the anti-septic effects of lysozyme in HMGB1-mediated inflammatory responses in vitro and in vivo. The data showed that lysozyme posttreatment suppressed LPS-mediated release of HMGB1 and HMGB1-mediated cytoskeletal rearrangement. Lysozyme also inhibited HMGB1-mediated hyperpermeability and leukocyte migration in human endothelial cells. In addition, lysozyme inhibited the HMGB1-mediated activation of Akt, nuclear factor-κB (NF-κB), extracellular regulated kinases (ERK) 1/2 and production of interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), and chemoattractant protein-1 (MCP-1) in HUVECs. Furthermore, lysozyme reduced the cecal ligation and puncture (CLP)-induced release of HMGB1, migration of leukocytes, septic mortality, and pulmonary damage in mice. Collectively, these results suggest lysozyme as a candidate therapeutic agent for the treatment of vascular inflammatory diseases via inhibition of the HMGB1 signaling pathway.