Cancer surgery is a major challenge for patients to develop immune depression in postoperative period. Several cytokines can depress immune cell subpopulations. Increased cytokine response after surgery is assumed to arise mainly from lipooxygenase pathway acting on membrane arachidonic acid. Therefore; investigators focused their efforts to alter the membrane fatty acid profile by changing the nutritional regimen with epsilon-3 fatty acid supplementation and encouraging results were obtained after surgery. Despite the theoretical and clinical advantage of enteral nutrition many surgeons remain committed to parenteral nutrition for feeding of patients due to maintain bowel rest and fear of anastomosis leakage at the postoperative period. Several studies investigating role of the postoperative immunonutrition reported that beneficial immunological changes were associated with reduction of infectious complications. Interestingly; these findings were observed at least five days after the surgery in which the highest incidence of complications was seen. In this prospective study including 42 patients eligible for curative gastric or colon cancer surgery; we investigated the beneficial effect of enteral immunonutrition (EEN) compared to total parenteral hyperalimentation (TPN) beginning from the preoperative period. Cortisol and CRP levels as stress parameters significantly increased one day after surgery in both groups but they rapidly returned to (on POW) preoperative baseline level in EEN group whereas these values remained high in the TPN group. Additionally a significant decrease in natural killer (NK) cells and CD8+ levels were observed in both groups. However they recovered on PODS in EEN group and on POD6 in TPN group. CD4+ subset remained almost same as preoperative value in the TPN group whereas it increased from (%) 40.14 to 46.40, 51.29 and 54.7 on PO 6(th) hr, POD3 and POD6 in the EEN group. Our findings suggest that preoperative nutrition via the enteral route provided better regulation of postoperative immune system restoration than parenteral nutrition. On the basis of our findings we recommend enteral immunonutrition to be started at the preoperative period rather than postoperatively before a major operation whenever the enteral route is feasible.