Objective:To assess the predictive value of the red blood cell distribution width(RDW) in evaluation of prognosis in severe acute pancreatitis patients. Methods:From January 2014 to January 2016,a total of 72 patients with severe acute pancreatitis were retrospectively analyzed. Comparisons for APHACH II score,SOFA score,RDW(RDWd1),procalcitonin,white blood cells,red blood cells,hemoglobin,serum amylase,albumin and C-reactive protein,which obtained at the first day after admission to ICU,were performed between survivors and non-survivors. The patients were divided into four groups according to RDWd1 value and RDWd3-d1(RDW at the third day-RDWd1). The Kaplan-Meier curve was used to evaluate the prognostic value of dynamic evolution of RDW for 90-days mortality. Log-rank test was performed to evaluate difference between groups. Results:Levels of APHACH II score,SOFA score,RDWd1 and procalcitonin on the first day were significantly higher in non-survivors(P < 0.001). In the univariate model,advanced age and RDWd1 were the independent risk factors of prognosis in SAP patients(OR=6.257,95%CI:1.539~25.440,P=0.010,and OR=2.554,95%CI:1.218~5.353,P=0.013). The optimal cut-off value of RDWd1 for predicting 90-days mortality was 14.8(the area under the ROC curve was 0.773,95%CI:0.652~0.893,P < 0.001). Patients with increased RDWd1 and RDWd3-d1>0.2% exhibited the highest risks for mortality(P=0.023). Conclusion:RDW and itself early dynamic elevation can be potential independent prognostic markers in patients with severe acute pancreatitis.