OBJECTIVE To investigate the value of macrophage migration inhibitor factor (MIF) in early severe acute pancreatitis (SAP). METHODS (1) Animal experiment: according to the random number table method, 24 male Sprague-Dawley (SD) rats were divided into Sham group and SAP 3, 6 and 12 hours groups, with 6 rats in each group. SAP rat model was prepared by injecting 5% sodium taurocholate via the retrograde cholangiopancreatic duct. Liver, kidney, lung, pancreas and serum samples were harvested after 3, 6 and 12 hours. In the Sham group, tissue and serum were harvested immediately after pancreas was turned over. The histopathological changes of the pancreas were observed microscopically by hematoxylin-eosin (HE) staining. The MIF levels of serum, liver, kidney, lung and pancreas were measured by enzyme linked immunosorbent assay (ELISA). (2) Clinical study: an observational study was conducted. Seventy-two adult patients within 24 hours of the onset of abdominal pain (blood amylase was 3 times the normal level), and the clinical diagnosis met the criteria of acute pancreatitis (AP) admitted to the emergency department of the First Affiliated Hospital of Zhengzhou University from December 2018 to October 2019 were enrolled. Venous blood was extracted and serum MIF level was determined by ELISA. Acute physiology and chronic health evaluation II (APACHE II) was recorded for 24 hours. Patients were divided into SAP group (17 cases), moderate severe acute pancreatitis (MSAP) group (25 cases), and mild acute pancreatitis (MAP) group (30 cases) according to the revised Atlanta criteria for comparison between groups. RESULTS (1) The results of animal experiments showed that the serum, liver, and pancreatic MIF levels of rats in the SAP group all reached the peak at 6 hours after modeling, and the differences were statistically significant compared with the Sham group [serum MIF (ng/L): 2 862.79±238.33 vs. 1 728.32±197.59, liver MIF (ng/L): 2 141.39±328.07 vs. 1 372.70±163.41, pancreas MIF (ng/L): 4 468.00±1 324.31 vs. 1 572.06±108.40, all P < 0.01]; although the levels of MIF in serum, liver and pancreas decreased at 12 hours after modeling, they were still significantly higher than Sham group. However, there was no statistically significant difference in MIF levels of lung and kidney in SAP rats compared with Sham group at 3, 6 and 12 hours after molding. (2) Clinical observation showed that early serum MIF levels of SAP, MSAP and MAP patients decreased in order, (14.83±2.99), (10.17±2.64), and (7.21±2.47) μg/L, respectively; APACHE II scores also decreased in order, 10.41±3.74, 7.60±3.18 and 4.00±2.41 respectively. Correlation analysis showed that serum MIF levels in patients with SAP, MSAP, and MAP had a good correlation with APACHE II scores of the respective groups, showing that MIF levels was positively correlated with disease severity (SAP: r = 0.51, P = 0.03; MSAP: r = 0.45, P = 0.02; MAP: r = 0.45, P = 0.01). CONCLUSIONS MIF can predict the occurrence of early SAP, and it is related to the severity of early AP.