No consensus has been reached concerning the effects of preoperative immunonutrition in patients undergoing hepatectomy. We evaluated the effects of immunonutrition before hepatectomy on perioperative management. This study was performed as a randomized controlled trial. Patients expected to undergo segmentectomy or more extensive hepatectomy for liver tumors were randomized to immunonutrition (IM) and control (C) groups each consisting of 13 patients. The IM group was given 750 ml of IMPACT in addition to half-size hospital meals orally from 5 days before to the day before surgery, and the C group was given conventional hospital meals. The blood level of eicosapentaenoic acid was elevated preoperatively in all patients of the IM group. The white blood cell count and interleukin 6 levels, which are indices of postoperative inflammation, were significantly lower in the IM group. As regards liver function, postoperative increases in the aspartate aminotransferase and alanine aminotransaminase levels were slightly suppressed in the IM group. No significant difference was noted in postoperative complications or duration of postoperative hospital stay. In patients undergoing hepatectomy, preoperative immunonutrition reduced inflammation and protected against liver dysfunction.