Background: Gastric adenocarcinoma (GA), one of the mostcommongastrointestinal cancers worldwide, is often accompanied by cancer cachexia in the advanced stage owing to malnutrition and cancer-related symptoms. Although resection is the most effective curative procedure for GA patients, it may cause perioperative fatigue, worsening the extent of cancer cachexia. Although the relationship between cytokines and cancer fatigue has been evaluated, it is unclear which cytokines are associated with fatigue in GA patients. Therefore, this study aimed to investigate whether the changes in cytokine levels were associated with the perioperative changes in fatigue amongst GA patients. Methods: We included GA patients undergoing gastric surgery in a single academic medical center between June 2017 and December 2018. Fatigue-related questionnaires, serum cytokine levels (interferon-gamma, interleukin (IL)-1, IL-2, IL-5, IL-6, IL-12 p70, tumor necrosis factor-alpha, and granulocyte-macrophage colony-stimulating factor), and biochemistry profiles (albumin, prealbumin, C-reactive protein, and white blood cell counts) were assessed at three time points (preoperative day 0 (POD 0), post-operative day 1 (POD 1), and postoperative day 7 (POD 7)). We used the Brief Fatigue Inventory-Taiwan Form to assess the extent of fatigue. The change in fatigue scores among the three time points, as an independent variable, was adjusted for clinicopathologic characteristics, malnutrition risk, and cancer stages. Results: A total of 34 patients were included for analysis, including 12 female and 22 male patients. The mean age was 68.9 years. The mean score for fatigue on POD 0, POD 1, and POD 7 was 1.7, 6.2, and 3.6, respectively, with significant differences among the three time points (P < 0.001). Among the cytokines, only IL-6 was significantly elevated from POD 0 to POD 1. In the regression model, the change in IL-6 levels between POD 0 and POD 1 (coeffcients = 0.01 for every 1 pg/mL increment; 95% confidence interval: 0.01–0.02; P = 0.037) and high malnutrition risk (coeffcients = 2.80; 95% confidence interval: 1.45–3.52; P = 0.041) were significantly associated with changes in fatigue scores. Conclusions: The perioperative changes in plasma IL-6 levels are positively associated with changes in the fatigue scores of GA patients undergoing gastric surgery. Targeting the IL-6 signaling cascade or new fatigue-targeting medications may attenuate perioperative fatigue, and further clinical studies should be designed to validate this hypothesis.