Background: Efficacy of adjuvant chemotherapy in stage II colon cancer patients is still controversial. The SACURA trial is a phase III study to evaluate the superiority of 1-year adjuvant treatment with oral tegafur-uracil (UFT) to surgery alone for stage II colon cancer in a large population. Methods: 20-80 aged patients with curatively resected stage II colon cancer were randomly assigned to the surgery alone group or UFT group (UFT at 500-600 mg/day as tegafur in 2 divided doses for 5 days, followed by 2-day rest, then repeated for 1 year). Primary endpoint was disease-free survival (DFS), and the secondary endpoints were overall survival (OS), recurrence-free survival (RFS), and safety. Sample size was 2000 determined with an assumed hazard ratio (HR) 0.729, respectively, a two-sided significance level of 5%, and a power of 90%. Results: A total of 1982 patients (997 in the surgery alone group and 985 in the UFT group) were included in the efficacy analysis. Median follow-up was 69.5 months, the median age at enrollment was 66 years, and stage IIA/IIB/IIC were 84%/13%/3%, respectively. The 5-year DFS rate was 78.4% in the surgery alone group and 80.2% in the UFT group. The HR for DFS was 0.91 (95%CI, 0.75-1.10; p = 0.307), and superiority of the UFT group was not demonstrated. Approximately 9% of patients in the both groups experienced second cancers, which consist 41.7% of the DFS events. The 5-year RFS rate was 84.6% and 87.2% (HR, 0.82; 95%CI, 0.65-1.04), and the 5-year OS rate was 94.3% and 94.5% (HR, 0.93; 95%CI, 0.66-1.31) in the surgery alone group and the UFT group, respectively. The completion rate of the 1-year UFT was 60.8%. The Incidence of grade 3/4 adverse events in the UFT group was 3.7% for ALT elevation, 3.3% for AST elevation, 1.4% for hyperbilirubinemia, 2.6% for anorexia, 1.9% for nausea, 1.4% for diarrhea, and < 1% for hematologic toxicities. Conclusions: Superiority of 1-year adjuvant treatment with UFT to surgery alone was not demonstrated in patients with stage II colon cancer. Clinical trial information: NCT00392899