We herein report a case of rupture of the urinary bladder due to emphysematous cystitis. The patient was an 77-year-old female who was hospitalized for treatment of a cerebral infarction and diabetes mellitus. Emphysematous cystitis was observed during examinations for fever. Despite urinary drainage and antibiotic therapy, she ran a fever for 3 weeks and had decreased urine volume. She was transferred to our hospital because a pelvic CT demonstrated intravesical gas, which suggested a diagnosis of a vesicorectal fistula. An emergency laparotomy was performed, and an extraperitoneal bladder rupture thus identified. She recovered under urinary drainage, ureterocutaneostomy, proper antibiotic therapy, and glycemic control. Although emphysematous cystitis is almost always cured with conservative therapy, an accurate diagnosis and proper treatment are required, because emphysematous cystitis may rarely result in the rupture of the urinary bladder.