Abstract： Objectives To determine the serum levels of high mobility group box-1 protein ( HMGB1 )in patients with acute pancreatitis (AP) and to investigate the contributions of HMGB1 in the pathogenesis of AP. Methods The serum HMGB1 concentrations were determined by enzyme-linked immunosorbent assay in 33 patients with severe acute pancreatitis (SAP), 38 patients with mild acute pancreatitis (MAP) and 28 healthy controls at the time of admission within 72 h after the onset. THe relationships between the serum HMGB1 levels and sex, age, etiology, disease onset, Ranson score, Balthazar CT score, C-reactive protein,lactate dehydrogenase and serum creatinine, total bilirubin levels, local and systematic complications were analized. Results The serum HMGB1 levels in healthy control group, MAP group and SAP group were ( 1.82 ±0.64)μg/L, (6. 13 ±5.80) μg/L and (11.48 ±6.94)μg/L, respectively. The mean value of serum HMGB1 level in MAP group was significantly higher than that in healthy group ( P < 0. 05 ), while it was significantly lower than that in SAP group ( P <0.05 ). Within 24 h after disease onset, the serum levels of HMGB1 began to increase, and reached the peak at 48 h, then decreased and remained higher than normal value at 72 h.There were no remarkable relationships between the serum HMGB1 levels and sex, age, etiology, but it was positively correlated with Ranson score, Balthazar CT score, C-reactive protein, lactate dehydrogenase and serum crkatinine. The serum levels of HMGB 1 in patients with local and / or systematic complications were higher than those in patients without complications, but the difference was not statistically significant.Conclusions HMGB1 is a late inflammation mediator and serum HMGB1 levels were correlated with the severity of AP. HMGB1 may participate in the development of acute renal insufficiency during SAP.