Background: Growing number of studies indicate tumor budding is a significant prognostic factor in colorectal cancer (van Wyk, et al. Cancer Treat Rev 2015), but this has been shown only in retrospective studies. We prospectively evaluated prognostic factors in stage II colon cancer to determine their prognostic value in a multi-institutional phase III study (SACURA trial, ASCO2016 abst#3617). Methods: A total of 991 patients with curatively resected stage II colon cancer (2006–2010; 136 institutions) were included in the study. Tumor budding was defined as an isolated cancer cell or a cluster composed of fewer than five cells in the invasive frontal region, and was graded based on its number within a microscopic field of a 20x objective lens (0.785 mm²) in the hotspot. Tumors with < 5, 5–9, and ≥10 budding foci were classified as grades G1, G2, and G3, respectively. All clinical and pathological data including the grade of budding were prospectively recorded and prognostic analyses were performed at 5 years after the completion of registration. Results: According to budding grading, 376, 331 and 284 tumors were classified as G1, G2, and G3, and 5-year relapse-free survival (RFS) rate was 90.9%, 85.1%, and 74.4%, respectively (P< 0.0001). Budding grade was significantly associated with the incidence of recurrence in the liver, lung, lymph node, and peritoneum (P< 0.0001–0.01). Among conventional factors, T stage and the serum CEA levels were associated with RFS, however, tumor grade, lymphatic and venous invasions, and the number of lymph node examined were not significant factors. Multivariate analysis for RFS showed budding, along with T stage, exerted an independent influence on prognostic outcome. Budding grade surpassed T stage and tumor grade in the ability to stratify patients by RFS (Harrell’s c-index, 0.63, 0.59, and 0.54, respectively). Conclusions: Our prospective study indicates that the grade of tumor budding is more informative for prognostic prediction than conventional prognostic factors in stage II colon cancer. The role of this prognostic factor should be highlighted in the adjuvant treatment setting, and conversely, some of prognostic factors adopted in clinical guidelines may need to be reconsidered. Clinical trial information: NCT00392899