Basic and clinical reports have suggested that eicosapentaenoic acid (EPA) exhibits anti-tumor activity. The present study evaluated whether perioperative EPA could improve the survival of patients with localized gastric cancer as a key secondary endpoint of a randomized clinical study. The present study was designed as multicenter, open-label, superiority, randomized trial to confirm the preventive effect of EPA on body weight loss after total gastrectomy for gastric cancer. Eligible patients were randomized to either the standard-diet group (EPA-off group) or EPA-on group by a centralized dynamic method. An EPA-enriched supplement (ProSure®) was given to the EPA-on group in addition to their standard diet. This supplement included 600 kcal with 2.2 g/day of EPA. Among the 126 patients who were randomized, 123 patients (EPA-off group, n=60; EPA-on group, n=63) were examined in the survival analyses. All background factors were well balanced between the two groups. The 3-year and 5-year overall survival rates were 74.6 and 67.8%, respectively, in the EPA-off group, and 77.8 and 76.2% in the EPA-on group. There was no significant difference between the EPA-off and EPA-on groups (hazard ratio, 0.77; P=0.424). In the subgroup analysis, the hazard ratio was 0.39 in patients who received neoadjuvant chemotherapy and 0.57 in patients with nodal metastasis. In conclusion, a clear survival benefit of perioperative EPA was not observed in localized gastric cancer. The value of EPA should be further tested in a future study in patients with unfavorable advanced gastric cancer. Clinical trial number: UMIN000006380; date of registration, September 21, 2011.