Background: Addition of perioperative multi-agent chemotherapy to the treatment strategy for locally advanced rectal cancer (LARC) may be a promising option. We conducted a multicenter single-arm phase II study to evaluate the safety and efficacy of capecitabine combined with oxaliplatin and irinotecan (CAPOXIRI) as triplet neoadjuvant chemotherapy in patients with LARC. Methods: The key eligibility criteria were as follows: (1) age over 20 years; (2) Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1; (3) resectable clinical stage II (T3 or T4 with N0) or III (any T and N1–3), with the primary tumor located within 12 cm of the anal verge. Patients received intravenous oxaliplatin (85 mg/m²) and intravenous irinotecan (150 mg/m²) on day 1 and oral capecitabine (1,000 mg/m²) twice daily on days 1–7 followed by 7 days of rest, repeated every 2 weeks for six cycles. Total mesothelial resection was performed 4–8 weeks after chemotherapy ended. In addition to the treatment protocol, patients received adjuvant chemotherapy for four cycles. The primary study endpoint was the pathological complete response (pCR) rate. We based the sample size of the study described herein on an expected pCR rate of 18% and a threshold pCR rate of 5% to detect differences at a two-sided alpha error of 0.05 and a statistical power of 0.2. Results: Between June 2013 and December 2016, 55 patients were enrolled in the study. Forty-five (83.3%) of the 54 patients who underwent NAC received the full six courses. Fifty-two (94.5%) patients underwent tumor resection. Laparoscopic surgery was performed in 47 (90.4%) patients, and lateral lymph node dissection was performed in 35 (67.3%) patients. Forty-nine (94.2%) patients underwent R0 resection. The pCR rate was 7.7% (95% CI 3.0% to 18.2%). The 3-year local recurrence rate was 3.9%, the 3-year disease-free survival (DFS) rate was 77.3, and the 3-year overall survival rate was 96.0%. NAC-related grade 3/4 adverse event rates were as follows: neutropenia (25.9%), anorexia (13.0%), diarrhea (11.1%) and anemia (7.4%). Conclusions: CAPOXIRI neoadjuvant chemotherapy appears to be feasible and efficacious for patients with LARC. Although neoadjuvant XELOXIRI alone did not yield our expected pCR rate, the local recurrence rate, 3-year DFS and measures of safety met current standards. Clinical trial information: UMIN000009974.