Objectives: The aim of this present study was to investigate the D-dimer in acute pancreatitis and its associations with triglyceride (TG). Methods: The D-dimer was measured in 45 patients with mild acute pancreatitis, 43 patients with severe acute pancreatitis, and 45 healthy controls. Eighty-eight patients were divided into high and low TG groups based on their TG levels. Twenty outpatients with serumal TG levels higher than 5.65 mM were chosen as hypertriglyceridemia controls. We investigated whether there were any correlations between the D-dimer levels and serumal TG in acute pancreatitis. Results: In 45 patients with mild acute pancreatitis, the D-dimer increased to approximately 2 times over the reference value, whereas in 43 patients with severe acute pancreatitis, the D-dimer level increased to 6 times above the limit; the difference was significant. Both TG and acute pancreatitis could cause an elevation of the D-dimer level, in which TG takes a more important role. The increase in the D-dimer was also directly related to the severity of acute pancreatitis. Conclusions: Plasma concentrations of the D-dimer increase in acute pancreatitis. The increase in TG is probably the main cause of the D-dimer elevation in patients with acute pancreatitis.