B ackground: Red blood cell distribution width (RDW) that describes red blood cell volume heterogeneity is a common laboratory test. Our aim was to focus on th e association between RDW and a c ute pancreatitis associated lung injury (APALI). Methodology: A total of 152 acute pancreatitis (AP) patients who conformed to the criteria w ere included in this study. The demographic data, medical histories and laboratory measures was obtained from each patient on admission, further, the medical histories and biological data were analyzed, retrospectively. Results: Increased RDW at admission was observed in patients with APALI compared with the non-APALI groups. Our results exhibited that RDW was an independent risk factor for APALI after adjusting leukocyte, neutrophil percentage, random blood glucose (RBG), total bilirubin (TB) and total bile acid（TBA）(Crude model) (OR=2.671;CI 95% 1.145-6.230; P=0.023), further adjustment based on Crude model for sex and age did not attenuate the significantly high risk of APALI in patients with AP, RWD still remained a ro les as an independent risk factor for APALI (OR=2.653;CI95 % 1.123-6.138; P=0.026). Conclusions: Our study demonstrate that RDW at admission is associated with APALI and should be considered as an underlying risk factor of APALI.