Background: The ACTS-CC trial, a randomized phase III trial, demonstrated that adjuvant therapy with S-1 for stage III colon cancer was non-inferior in 3-year disease-free survival (DFS) to that of tegafur-uracil plus leucovorin (UFT/LV). We updated DFS and overall survival (OS), and performed some clinically relevant subgroup analyses. Methods: A total of 1,535 patients with stage III colon cancer were randomly assigned to receive S-1 (80-120 mg/day on days 1-28 every 42 days, 4 courses) or UFT/LV (UFT: 300- 600 mg/day and LV: 75 mg/day on days 1-28 every 35 days, 5 courses). Primary endpoint was DFS. Secondary endpoints were OS and safety. Results: A total of 1518 patients (758 in the S-1 group and 760 in the UFT/LV group) were included in the efficacy analysis. Median follow-up was 63.5 months, the mean age at enrollment was 64.5 years, wide lymph node dissection (D3) was done in 79.8%, the median number of dissected lymph nodes was 17, and stage IIIA/IIIB/IIIC were 15%/71%/14%. The hazard ratio (HR) for DFS was 0.88 (95%CI, 0.74-1.06; p = 0.177). The 5-year DFS rate was 70.2% in the S-1 group and 66.9% in the UFT/LV group. In the subgroup analysis, no significant interactions were identified between the major baseline characteristics and the DFS in S-1 and UFT/LV, except for histological type; favors S-1 in patients with poorly-differentiated adenocarcinoma. Approximately 5% of patients in the both groups experienced second cancers. Among the patients with recurrences in each group, 46.3% and 44.7% underwent surgical resection as an initial treatment for recurrence. The HR for OS was 0.92 (95%CI, 0.72-1.17; p = 0.488). The 5-year OS rates were 86.0% and 84.4% in the S-1 and UFT/LV group, respectively. Conclusions: Adjuvant therapy of S-1 for stage III colon cancer was confirmed to be non-inferior both in DFS and OS to those of UFT/LV after long follow-up. Favorable OS might be brought by the high resection rate of recurrent lesions. Clinical trial information: NCT00660894