A 66-year-old man with a history of frequent diarrhea was diagnosed with rectal cancer with obstruction and a pelvic abscess. Following a transverse colostomy, he was referred to our hospital. The initial diagnosis was rectal cancer(cT4a N1bM0, cStage Ⅲb)and a pelvic abscess due to tumor perforation. To address this condition, we performed neoadjuvant chemotherapy using a combination of 5-fluorouracil, Leucovorin, oxaliplatin, and irinotecan(FOLFOXIRI). Following 6 courses of FOLFOXIRI, the abscess disappeared and no signs of tumor progression and distant metastases were detected. Subsequently, we performed radical resection with D3LD2 lymph node dissection, leading to a pathological diagnosis of ypT3N1aM0, ypStage Ⅲb. The patient then underwent adjuvant chemotherapy with capecitabine and oxaliplatin(CAPOX). No recurrence was observed after 9 months of follow-up.