Two cases of Fournier's gangrene occurred during chemotherapy for advanced rectal cancer. Patients were treated using surgical debridement and antibiotic therapy. Case 1: A 66-year-old man had advanced rectal cancer with para-aortic and inguinal lymph node metastases. He received a sigmoid colostomy and chemotherapy(capecitabine, oxaliplatin, bevacizumab). Due to progression of the rectal mass, we performed radiotherapy(30 Gy)and chemotherapy(irinotecan, S-1, bevacizumab). After 14 days, he was hospitalized with a diagnosis of Fournier's gangrene with anal pain and fever. Case 2: A 63-year-old man had mucinous rectal carcinoma with sacrum invasion. He received a sigmoid colostomy and chemotherapy. Sixteen days after regorafenib therapy, as a fifth-line of chemotherapy, he was hospitalized with a diagnosis of Fournier's gangrene with hip pain, swollen perineum, and fever. There have been no reports of Fournier's gangrene occurring during chemotherapy for rectal cancer. We report 2 cases with a review of literature.