Background: Tumors and surgical procedures trigger a series of metabolic responses that put gastric cancer patients at constant risk of malnutrition during the perioperative period. Meanwhile, the effectiveness of enteral immunonutrition (EIN) for these patients remains a subject of ongoing debate. Objective: This systematic review and evidence map aim to retrieve randomized controlled trials (RCTs) on perioperative EIN interventions in gastric cancer patients undergoing surgery and evaluate their effectiveness. Methods: A systematic search strategy was established using the Population, Intervention, Comparison, Outcomes and Study design (PICOS) framework to identify relevant RCTs evaluating EIN for gastric cancer surgery patients. The databases searched were PubMed, Web of Science, Embase, CINAHL, and CENTRAL (Cochrane Library), covering studies published up to September 30, 2024. Two reviewers independently screened titles and abstracts. The quality of the studies was assessed using the Cochrane Risk of Bias Tool version 2 (RoB 2). Data were independently extracted and descriptively synthesized, with the results summarized in an evidence gap map. Results: In this systematic review, 20 studies that met the inclusion criteria were included, focusing on the effects of perioperative EIN on patients with gastric cancer. The interventions involved various immunonutrients such as arginine, omega-3 fatty acids, glutamine, and ribonucleic acid, with different initiation times ranging from preoperative to postoperative, and durations ranging from 5 to 28 days. Most studies used EN as the control, while some used PN. The risk of bias assessment revealed that three studies had a high risk of bias, primarily due to issues with randomization. The majority of studies focused on changes in immune function and inflammatory markers, with some also evaluating postoperative infection complications or other clinical outcomes. The evidence gap map (EGM) analysis showed that although postoperative interventions were more common, only 45.45 % of these studies demonstrated a "positive impact", while the remaining studies indicated a "possible positive impact" or "no effect". Overall, EIN interventions showed some positive effects on immune function and inflammatory markers, but results varied across studies. Conclusions: This review summarized the effects of perioperative EIN in gastric cancer surgery patients, highlighted existing gaps and suggested future research to optimize its application. (c) 2025 The Author(s). Published by Elsevier Ltd on behalf of European Society for Clinical Nutrition and Metabolism. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).