Background Sepsis is a leading cause of death in the intensive care units. The late inflammatory cytokine,high-mobility group box 1 (HMGB1), plays a critical role in sepsis. In the present study, we investigated the association between the serum HMGB1 levels and the severity of organ injury in the lipopolysaccharide-induced sepsis in rats.Methods To produce an animal model of sepsis with different degree of organ injury, animals were treated with three different doses of lipopolysaccharide (4, 8 and 16 mg/kg), and the animals in control group were treated with the same volume of the vehicle (saline). The levels of serum HMGB1 were measured at 0, 2, 4, 8, 16, 24, 32 and 48 hours after lipopolysaccharide (LPS) or vehicle injection, meanwhile the biochemical and histopathological indicators for the severity of organ injury were assessed.Results The level of HMGB1 had a positive, high correlation with the abnormal changes of serum cardiac troponin Ⅰ, alanine aminotransferase, aspartate aminotransferase, creatinine and blood urea nitrogen, as well as the pathologic scores of heart, lung, liver and kidney.Conclusions The level of serum HMGB1 is highly correlated with the severity of sepsis in rats, suggesting that HMGB1 could serve as a valuable adjunct in the diagnosis and management of sepsis.