Objective Pancreatic enzymes may spread into the injured intestine, bloodstream,and cause the cascade of inflammatory reactions. Our objective was to explore trypsin expression in serum and vital organs in septic rats. Methods Trypsin levels in serum, heart, lung and jejunum were tested and compared between Escherichia coli endotoxin injected rats(SS), SS treated with a protease inhibitor (ulinastatin) and control group(SHAM). The correlations between serum trypsin, intestinal proteins and inflammation indices were assessed.Two components of mucosal barrier, i.e. mucin-2 and E-cadherin,were measured to evaluate the intestinal mucosal barrier function. The levels of tumor necrosis factor alpha (TNFα), interleukin-6(IL-6) and neutrophil elastase(NE) were measured to determine the inflammation indices.Results Compared to SHAM group, trypsin levels in serum[(73.71±9.14) ng/ml vs. (12.12±2.36) ng/ml],heart[(51.60±15.06) ng/ml vs. (6.39±3.53) ng/ml],lung [(54.73±5.57) ng/ml vs. (5.24±3.08) ng/ml] and jejunum(1.19 ± 0.48 vs. 0.40 ± 0.12) were significantly higher in SS group (all P<0.05). The level of serum trypsin had negative correlation with mucin-2 and E-cadherin, and positive correlation with TNFα, IL-6 and NE (all P<0.05). In rats treated with ulinastatin, trypsin levels were significantly decreased compared with those in SS group including in serum [(65.79±4.88)ng/ml]], heart [(26.33±12.03)ng/ml], lung [(28.73±14.46) ng/ml] and jejunum (0.80±0.20) (all P<0.05).Serum TNFα[ (247.34±16.97)ng/L vs. (178.78±40.81)ng/L] revealed similar changes in ulinastatin and SS group, whereas mucin-2(0.58 ± 0.14 vs. 0.89 ± 0.17)and E-cadherin(0.11 ± 0.04 vs. 0.23 ± 0.06)were both significantly elevated after administration of ulinastatin (both P<0.05). Conclusion Serum and tissue trypsin is elevated in septic rats. Protease inhibitor ulinastatin protects intestinal function by reducing inflammatory reaction.