BACKGROUND To investigate the effects of early enteral nutrition (EEN) on intra-abdominal pressure (IAP) and disease severity in patients with severe acute pancreatitis (SAP). METHODS Enteral nutrition (EN) was started within 48 h after admission in the EEN group and from the 8th day in the delayed enteral nutrition (DEN) group. The IAP and intra-abdominal hypertension (IAH) incidence were recorded for 2 weeks. The caloric intake and feeding intolerance (FI) incidence were recorded daily after EN was started. The severity markers and clinical outcome variables were also recorded. RESULTS Sixty patients were enrolled to this study. No difference about IAP was found. The IAH incidence of the EEN group was significantly lower than that of the DEN group from the 9th day (8/30 versus 18/30; P = 0.009) after admission. The FI incidence of the EEN group was higher than that of the DEN group during the initial 3 days of feeding (25/30 versus 12/30; P = 0.001; 22/30 versus 9/30; P = 0.001; 15/30 versus 4/30; P = 0.002). Patients with an IAP <15 mmHg had lower FI incidence than those with an IAP ≥15 mmHg on the 1st day (20/22 versus 17/38; P < 0.001), the 3rd day (11/13 versus 8/47; P < 0.001), and the 7th day (3/5 versus 3/55; P = 0.005) of feeding. The severity markers and clinical outcome variables of the EEN group were significantly improved. CONCLUSIONS Early enteral nutrition did not increase IAP. In contrast, it might prevent the development of IAH. In addition, EEN might be not appropriate during the initial 3-4 days of SAP onset. Moreover, EN might be of benefit to patients with an IAP <15 mmHg. Early enteral nutrition could improve disease severity and clinical outcome, but did not decrease mortality of SAP.