The aim of this study was to evaluate clinical and economic validity of perioperative immunonutrition and effect on postoperative immunity in patients with gastrointestinal cancers. Immunonutrition diet supplemented two or more of nutrients including glutamine, arginine, omega-3 polyunsaturated fatty acids and ribonucleic acids. A meta-analysis of all relevant clinical randomized controlled trials (RCTs) was performed. The trials compared perioperative immunonutrition diet with standard diet. We extracted RCTs from electronic databases: Cochrane Library, MEDLINE, EMBASE, SCI and assessed methodological quality of them according handbook for Cochrane reviewer in June 2006. Statistical analysis was performed by RevMan4.2 software. Thirteen RCTs involving 1269 patients were included. The combined results showed that immunonutrition had no significant effect on postoperative mortality (OR = 0.91, p = 0.84). But it had positive effect on postoperative infection rate (OR = 0.41, p<0.00001), length of hospital stay (WMD = -3.48, p<0.00001). Furthermore, it improved immune function by increasing total lymphocytes (WMD = 0.40, p<0.00001), CD4 levels (WMD = 11.39, p<0.00001), IgG levels (WMD = 1.07, p=0.0005) and decreasing IL6 levels (WMD = -201.83, p<0.00001). At the same time, we did not found significant difference in CD8, IL2 and CRP levels There were no serious side effects and two trials found low hospital cost. In conclusion, perioperative diet adding immunonutrition is effective and safe to decrease postoperative infection and reduce length of hospital stay through improving immunity of postoperative patients as compared with the control group. Further prospective study is required in children or critical patients with gastrointestinal surgery.