Objective：This study aimed to assess the value of neutrophil to lymphocyte ratio（NLR）in predicting the severity of acute biliary pancreatitis（ABP）and pancreatic necrosis（PN）. Methods：A total of 290 ABP patients were included in this study. The blood samples were collected for examination of blood routine and related biochemical indicators within 24 hours after onset of acute pancreatitis. The optimal cut-off value for NLR to predict severe acute pancreatitis（SAP）and PN was determined by receiver operating characteristic（ROC）curve analysis. ABP model was induced by taurocholic acid sodium in rats，and the blood and pancreatic tissue were collected in 1，3，5，7，14 days after modeling to compare the NLR among groups. Results：ROC curve showed that NLR had a predictive performance for SAP［area under the curve（AUC）：0.944，95%CI：0.915-0.973，P < 0.001］，the optimal cut-off from ROC curve was 13.38（sensitivity：80.0%；specificity：83.2%）. For the prediction of PN，the AUC of NLR was 0.910（95%CI：0.861-0.958， P < 0.001），the cut-off value was 9.265（sensitivity：97.1%；specificity：72.7%）. In ABP rats，NLR increases in the early stages of AP and is correlated with the severity of AP and PN. Conclusion：Within 24 h after the onset of ABP，NLR can be used as a powerful for early prediction of its severity and PN.