Background: Preoperative 5-FU-based chemoradiation is currently a standard treatment for advanced rectal cancer, particularly in Western countries. Although it reduced the local recurrence, it could not necessarily improve overall survival. Furthermore, it can also produce adverse effects and long-term sphincter function deficiency. Adjuvant oxaliplatin plus capecitabine (XELOX) is a recommended regimen for patients with curatively resected colon cancer. However, the efficacy of postoperative adjuvant therapy for rectal cancer patients who have not undergone preoperative chemoradiation remains unknown. We aimed to evaluate the efficacy of surgery and postoperative XELOX without preoperative chemoradiation for treating rectal cancer. Methods: We performed a prospective, multicenter, open-label, single arm phase II study. Patients with curatively resected high-risk stages II and III rectal cancer who had not undergone preoperative therapy were treated with a 120 min intravenous infusion of oxaliplatin (130 mg/m²) on day 1 and capecitabine (2,000 mg/m²/day) in 2 divided doses for 14 days of a 3-week cycle, for a total of 8 cycles (24 weeks). The primary endpoint was 3-year disease-free survival (DFS). Results: Between August 2012 and June 2015, 60 men and 47 women with a median age was 63 years (range: 29–77 years) were enrolled. Ninety-three patients had Eastern Cooperative Oncology Group performance status scores of ‘0’ and 14 had scores of ‘1’. Tumors were located in the upper and lower rectums in 54 and 48 patients, respectively; 8 patients had stage II disease and 99 had stage III. The 3-year DFS was 70.1% (95% confidence interval, 60.8–78.0%) and 33 patients (31%) experienced recurrence, most commonly in the lung (16 patients) followed by local recurrence (9) and hepatic recurrence (7). Conclusions: Postoperative XELOX without preoperative chemoradiation is effective for rectal cancer and provides good 3-year DFS prospects.And this is probably the first and last report in the world for such cases. Trial registration: This clinical trial was registered in the University Hospital Medical Information Network registry system as UMIN000008634 at Aug 06, 2012.