Abstract: OBJECTIVE To observe the effect of prophylactic use of compound amino acid injection on reduction of incidence of postoperative infection and improvement of immune function of gastric cancer patients undergoing radical gastrectomy. METHODS A total of 80 patients who received the radical gastrectomy in the hospital from Dec 2012 to Nov 2017 were enrolled in the study and randomly divided into the experimental group and the control group in a 1:1 ratio, with 40 cases in each group. Both groups were given the same conventional therapy, the experimental group was treated with the compound amino acid injection prophylaxis. The incidence of postoperative infection was compared between the two groups of patients, and the levels of albumin, hemoglobin, inflammatory factors and immunological indexes were observed and compared between the two groups of patients before the surgery and after the surgery for 1 and 3 days. RESULTS The incidence rate of postoperative infection of the experimental group was 2.50％, significantly lower than 12.50% of the control group (P=0.031). The albumin level of the experimental group was significantly higher than that of the control group (P<0.05). The levels of albumin and hemoglobin of the experimental group were significantly higher than those of the control group, and the IL-6 level of the experimental group was significantly lower than that of the control group (P<0.05). The levels of CD₃⁺ and CD₄⁺ of the experimental group were reduced more significantly than those of the control group after the surgery for 1 and 3 days, and the CD8+ level of the experimental group was elevated less significantly than that of the control group (P<0.05). CONCLUSIONS The prophylactic use of compound amino acid injection may reduce the consumption of proteins and improve nutrition status of the patients undergoing the radical gastrectomy so as to boost the immune function, prevent the postoperative infection, which provides a novel method for prevention of the postoperative infection, reduces the use of antibiotics and improve the anti-infection effect.