Klebsiella pneumoniae ( K. pneumoniae ) can at times cause invasive infections, especially in patients with diabetes mellitus and a history of alcohol abuse. A 61-year-old man with diabetes mellitus and a history of alcohol abuse presented with abdominal and anal pain for two weeks. After admission, he underwent sigmoidoscopy, which revealed multiple ulcerations with yellowish exudate in the rectum and sigmoid colon. The patient was treated with ciprofloxacin and metronidazole. After one week, follow up sigmoidoscopy was performed owing to sustained fever and diarrhea. The lesions were aggravated and seemed webbed in appearance because of damage to the rectal mucosa. Abdominal computed tomography and rectal magnetic resonance imaging were performed, and showed a perianal and perirectal abscess. The patient underwent laparoscopic sigmoid colostomy and perirectal abscess incision and drainage. Extended-spectrum beta-lactamase-producing K. pneumoniae was identified in pus culture. The antibiotics were switched to ertapenem. He improved after surgery and was discharged. K. pneumoniae can cause rapid invasive infection in patients with diabetes and a history of alcohol abuse. We report the first rare case of proctitis and perianal abscess caused by invasive K. pneumoniae infection.