Objective This study was conducted to evaluate the effects of postoperative immune enhancing enteral nutrition on the immune system, inflammatory responses, and clinical outcome of patients undergoing major abdominal surgery. Methods This study was designed as a multicenter, prospective,randomized and controlled clinical trial. One hundred twenty-four patients undergoing major abdominal surgery were randomly assigned to receive either an immune enhancing enteral diet or an isocaloric and isonitrogenous control enteral diet for seven days. Enteral feeding was initiated 24 hours after surgery. Host immunity was evaluated by measuring levels of IgG, IgM, IgA, CD4, CD8, and CD4/CD8, and the inflammatory response was determined by assessing IL-1α, IL-2, IL-6, IL-10, and TNF-α levels. Infectious complications were also recorded. Results One hundred twenty patients completed the study and four patients were excluded. On postoperative day 9, among patients receiving an immune enhancing diet,IgG, IgA, CD4 and CD4/CD8 levels were significantly higher and TNF-α and IL-6 concentrations were significantly lower compared to the control group. Moreover, among patients receiving an immune enhancing diet, when comparing preoperation to day 9 postoperation levels, increases in IgA, CD4, and CD4/CD8 levels were significantly higher than in control patients and increases in TNF-α concentrations were significantly lower. No statistically significant differences were found between the two groups with regard to infectious complications.Conclusions Postoperative administration of immune enhancing enteral nutrition in patients undergoing major abdominal surgery can positively modulate postoperative immunosuppressive and inflammatory responses.