A considerable amount of data suggests that postoperative infectious complications result from malnutrition, organ impairment, and metabolic disorders. Since metabolism may become deranged once a complication occurs, appropriate pre- and postoperative nutritional support is very important for preventing postoperative infections. For patients who experience postoperative infections such as peritonitis, pyothorax, mediastinitis, or pneumonia, a special feeding formula for the metabolic derangement observed in sepsis and organ impairment should be administered. Branched-chain amino acids (BCAAs) are considered to reduce protein catabolism during the course of a septic insult. A BCAA-enriched parenteral nutrition formula is preferable for patients who cannot receive enteral feeding. Enteral nutrition should always be given the first priority in patients with a functional intestinal tract who are unable to consume adequate calories orally. Enteral formulas can include special nutrients such as dietary fiber and glutamine-analog which exert a trophic effect on the gut mucosa or enhance immunocompetence.