Abstract： Objective To evaluate the changes of blood coagulation and their clinical significance in pa-tients with severe acute pancreatitis (SAP). Method Two hundred and seven patients with acute pancreatitis ad-mitted from January 2005 to Deeember 2008 in People' s Hospital, Peking University, were recruited in this study. Patients were divided into two groups, severe acute pancreatitis (53 cases) and mild acute pancreatitis (154 cas-es), according to the diagnostic criteria set by the Chinese Medical Association in 2004. Plasma coagulation pa-rameters including prothrombin time (PT), prothrombin activity (PTA), international normalized ratio (PT-INR), activated partial thromboplastin time (APTT), fibrinogen (FIB) and D-dimmer were redorded. Results Com-pared with MAP group, there were significant differences on PT, PTA, PT-INR, FIB, and D-dimmer in SAP group [in MAP group, (12.45 ± 1.13) s,(94.01±21.21)% ,(1.08±0.14),(4.81±1.86)g/L,340.38 ng/ mL, respectively;in SAP group, (13.08±1.47)s,(86.92±17.36) %, (1.14±0.20), (5.49±2.30)g/L, 943.82 ng/mL, respectively; P <0.05]. There was no significant difference on APTT between the two groups (P > 0.05). D-dimmer was correlated to the APACHE Ⅱ score , and it was also correlated to the SIRS score (P < 0.05). The rate of systemic inflammatory response syndrome (SIRS) and the mortality were higher in patients with SAP patients than those in the MAP patients (in SAP group, 35.5%, 5.6%, respectively; in MAP group, 10.4%, 0, respectively; P < 0.05). Conclusions Disorders of coagulation and microcirculation disturbances were observed in patients with severe acute pancreatitis. These alterations may be useful in the assessment of the disease severity and prognosis of patients with acute pancreatitis.