Objective: To investigate the serum angiopoietin-Ⅱ (Ang Ⅱ) levels in acute pancreatitis (AP) patients and the relationship between AngⅡ levels and the disease severity of AP based on the new Atlanta classification criteria. Methods: Seventy-seven patients with AP who were treated in the Affiliated Baiyun Hospital of Guizhou Medical University were included in this prospective study. According to the revised Atlanta classification, the modified Mashall scoring system was used to divided patients into AP with the persistent organ failure(POF) group and without POF group, and the CECT was used to divided patients into AP with pancreatic necrosis(PN) group and without PN group. The levels of AP 72 h after admission of two groups were compared with t test, and Spearman analysis was used to analyze the correlation between common severity indicators and Ang Ⅱ. The receiver operating characteristic (ROC) was performed to analyze the area under curve(AUC), sensitivity and specificity of Ang Ⅱ in predicting POF and PN. Results: According to the modified Mashall scoring system, there were 18 patients (23.38%) in POF group and 59 patients (76.62%) in without POF group. According to CECT, 22 patients (28.57%)were in PN group and 55 patients(71.43%) in without PN group. The Ang Ⅱ of the POF and PN groups was significantly higher than those without POF and PN groups (P=0.001, 0.011) on day 1 on admission. The cut-off value was 126.44 μg/L, and the AUC, sensitivity and specificity for predicting POF were 0.739, 83.3% and 68.4%, which was significantly better than that of traditional predictive indicators, such as C-reaction protein (CRP), procalcitonin (PCT), blood urea nitrogen (BUN), bedside index for severity in AP (BISAP) score and Ranson score. When the cut-off value was 130.90 μg/L, the AUC, sensitivity and specificity for predicting PN were 0.703, 77.3% and 73.6%, respectively, which was significantly better than that of all traditional single indicator. The predicted value was less than PCT and CRP 2 or 3 day after admission. In addition, the Ang Ⅱlevel 1 day after admission was closely related to the Ranson score, BISAP score, and PCT level which was commonly used indicators of AP severity. Conclusions Under the new Atlanta classification criteria, Ang Ⅱ is superior to the traditional predictive indicators commonly used for predicting POF, and is a better single biochemical indicator for predicting PN in clinic.