Background and Aims Proper nutritional support can provide essential nutrients and promote the recovery of patients after gastrointestinal tumor surgery. Adding alanyl-glutamine (Ala-Gln) to parenteral nutrition has been shown to improve clinical outcomes in patients. However, there are significant differences in the recommended concentration of Ala-Gln in parenteral nutrition in domestic and international drug manuals and clinical practice. Therefore, this study aims to investigate the effects of different ratios of Ala-Gln in parenteral nutrition on postoperative nutrition, liver and kidney function, and inflammation/immune status in gastrointestinal tumor patients to guide the standardized use of Ala-Gln.Methods This study was a randomized controlled clinical trial conducted on gastrointestinal tumor patients receiving postoperative parenteral nutrition support from June 2021 to April 2022 in the Department of Gastrointestinal Surgery, Xiangya Hospital, Central South University. Patients were randomly assigned to either the low ratio group (Ala-Gln dosage in enteral nutrition accounts for 20% of total amino acids) or the high ratio group (Ala-Gln dosage in enteral nutrition accounts for 30% of total amino acids). Both groups received parenteral nutrition support through central venous infusion starting the first day after surgery (once daily, lasting 8-12 h). Nutritional indicators, liver and kidney function parameters, and inflammation/immunity variables were monitored before surgery and on the first day after parenteral nutrition. Patient data on postoperative infections/complications, length of hospital stay, and in-hospital costs were collected from the hospital information system.Results A total of 77 patients were enrolled in this study, with 39 in the low ratio group and 38 in the high ratio group. The two groups had no statistically significant differences in baseline characteristics, preoperative nutritional indicators, liver and kidney function parameters, and inflammation/immunity variables (all P>0.05). Analysis of variance with repeated measurement tests showed that on the first day after enteral nutrition, all patients had a significant decrease in prealbumin, total protein, serum albumin, hemoglobin, total bile acid levels, as well as T lymphocytes (CD3⁺, CD4⁺, CD8⁺), immunoglobulins (IgG, IgA, IgM) levels compared to preoperative values; total bilirubin, direct bilirubin, aspartate aminotransferase, alanine aminotransferase, and urea levels, as well as inflammatory markers, the Th/Ts ratio, and complement C4 levels, were significantly higher after surgery compared to preoperative values (all P<0.05); only the Th/Ts ratio in the high ratio group was significantly higher than that in the low ratio group (P=0.026), while the differences in other indexes between the two groups were not statistically significant (all P>0.05). Total protein (P=0.032) and serum albumin (P=0.008) showed a significant interaction between the group and time. Multivariate linear regression analysis further indicated that the grouping had no significant impact on total protein and serum albumin levels (both P>0.05). There were no statistically significant differences in the incidence of postoperative infections/complications, length of hospital stays, and in-hospital costs between the two groups (all P>0.05).Conclusion The addition of different ratios of Ala-Gln in parenteral nutrition (20% of total amino acids vs. 30% of total amino acids) had no significant impact on the nutrition, liver and kidney function parameters, and postoperative recovery of gastrointestinal tumor patients. However, higher proportions of Ala-Gln had a better immunomodulatory effect on T lymphocytes. Clinical decisions should be based on individual patient needs to choose the appropriate ratio of Ala-Gln concentration.