Colovesical fistula is a rare complication of inflammatory or neoplastic disease, and traumatic or iatrogenic injuries. Among them, sigmoid diverticulitis is the most frequent cause of colovesical fistula. There are few reported cases of the colovesical fistula in Korean literature, that is probably because the left colonic diverticulum is not common in Korea. We present here a case of patient with colovesical fistula complicated by sigmoid diverticulitis. A 66-year-old male patient was transferred to our hospital due to complaining of abdominal pain and mucoid stool. An abdominal and pelvic CT scan revealed diverticulitis and peridiverticular abscess in sigmoid colon. The patient was admitted and treated with intravenous antibiotic agents for four weeks, followed by oral antibiotic therapy. Six weeks after being discharged from the hospital, he was admitted again with complaints of pneumaturia, fecaluria, and dysuria. Follow up CT scan demonstrated fistula between sigmoid colon and bladder dome portion. Under the diagnosis of colovesical fistula due to diverticulitis of sigmoid colon, low anterior resection and partial cystectomy with cystostomy were performed.