A 51-year-old man underwent abdominoperineal resection for advanced rectal cancer at a hospital. He attended our outpatient clinic 58 months later with pain in the external genitalia, and was diagnosed with local pelvic recurrence and metastasis to the para-aortic lymph node and both adrenal glands. He received a total of 30 Gy of radiation for analgesia; subsequently, chemotherapy(mFOLFOX6 plus bevacizumab)was initiated. However, extreme left buttock and left femoral pain developed after the 6 courses of chemotherapy. Abdominal CT revealed Fournier's gangrene caused by small intestinal perforation. Emergency drainage under spinal anesthesia was immediately performed. Two additional drainage procedures were required thereafter and an ileostomy was constructed. The patient was discharged 100 days after the initial drainage. This is an extremely rare example of a bevacizumab-related small intestinal perforation that developed into Fournier's gan- grene.