Objective To investigate the effects of enteral immunonutrition supplemented with omega-3 polyunsaturated fatty acid (ω-3 PUFA) on inflammatory response, intestinal mucosal barrier function and the prognosis in patients with severe traumatic brain injury (sTBI). Methods 122 patients of sTBI hospitalized between January 2015 and December 2016 were randomly divided into experimental group (ω-3 PUFA, n=61) and control group (n=61). The serum levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and neuron specific enolase (NSE) were tested with enzyme linked immunosorbent assay. Meanwhile, D-lactate acid and intestinal fat acid binding protein (I-FABP) were evaluated by enzymology spectrophotometer method. After 14 days of treatment, the Glasgow Coma Scale (GCS) scores, Acute Physiology and Chronic Health Evaluation (APACHE) Ⅱ scores and prognoses of both groups were compared. Results The serum levels of inflammatory factors (TNF-α and IL-6), intestinal mucosal barrier function indicators (D-lactate acid and I-FABP) and NSE proteins significantly increased after sTBI (P=0.01). Compared with the control group, the experimental group on day 3 had significantly lower serum levels of inflammatory factors [TNF-α: (107.77±19.79)μg/L vs. (151.76±21.65)μg/L, P=0.01; IL-6: (76.85±7.15)μg/L vs. (105.27±10.12)μg/L, P=0.01] and intestinal mucosal barrier function indicators [D-lactate: (69.81±6.32)μg/L vs. (89.80±8.75)μg/L, P=0.03; I-FABP: (40.81±6.73)μg/L vs. (56.60±8.58)μg/L, P=0.01]. On day 7, the experimental group had significantly lower expression of NSE proteins than the control group [(13.63±2.53)μg/L vs. (19.12±3.00)μg/L, P=0.02]. The experimental group received better prognosis compared to the control group on day 14 [GCS scores: (9.74±0.76)vs. (8.44±0.53), P=0.04; APACHE Ⅱ scores: (14.67±1.37)vs. (17.53±1.47), P=0.03]. The experimental group also had fewer days in hospitalization [(19.37±2.27)d vs. (25.42±2.61)d, P=0.01]. Conclusion Enteral immunonutrition supplemented with ω-3 PUFA can effectively regulate the inflammatory response, and reduce impairment to the intestinal mucosal barrier function and damage to neurons in patients with sTBI. Key words: Craniocerebral trauma; Unsaturated fatty acids; Inflammatory response; Intestinal mucosal barrier