Abstract: Objective To investigate the expression of high-mobility group box chromosomal protein 1(HMGB1) in patients with acute pancreatitis (AP) and its clinical value. Methods We measured blood HMGB1 mRNA levels by RT-PCR and serum HMGB1,TNF-α and IL-6 concentrations by an enzyme-linked immunosorbent assay in 20 patients with mild AP (MAP), 10 patients of severe acute pancreatitis without organ dysfunction (SAP-1), 10 patients of SAP with organ dysfunction (SAP-2). Furthermore, relationship between their serum HMGB1 levels and severity of AP was analyzed. Results The mean value of serum HMGB1 concentrations in patients with MAP, SAP-1 and SAP-2 were 3.5 ± 0.8 , 5.7 ± 1.6 and 8.3 ± 1.7 ng/mL respectively and were significantly higher than that in healthy subjects 1.6 ± 0.4 ng/mL. Blood HMGB1 mRNA levels in patients with MAP, SAP-1 and SAP-2 were 0.56±0.11，0.71±0.07，0.89±0.09 respectively and were significantly higher than that in healthy subjects 0.25±0.04. Serum HMGB1 levels and HMGB1 mRNA were significantly increased in patients with AP and were correlated with disease severity. Conclusion These results suggest that HMGB1 may act as a key mediator for inflammation and organ failure in AP.