A 54-year-old female who had been receiving continuous ambulatory peritoneal dialysis therapy for 5 years because of end-stage renal disease, was admitted to hospital because of peritonitis due to Candida albicans. Ultrasonography showed locular fluid in abdominal subcutaneous tissue. E. coli was isolated from the peritoneal fluid culture and cephoperazone-sulbactam therapy was started. Nose bleeding manifested on the 9th day after initial treatment. Prothrombin time, activated partial thromboplastin time, and INR were found to be 61.1 sec, 159.2 sec, and 5.55, respectively. She had no liver disease, obstructive jaundice, or other disease disrupting the intestinal absorption of vitamin K. Hepatitis markers were negative and liver function tests were normal. Warfarin and conventional heparin were also not used. The coagulation disorder was attributed to treatment with cephoperazonesulbactam and the treatment was discontinued. The bleeding stopped with intravenous vitamin K and fresh frozen plasma and the coagulation tests returned to normal range. Empirical meropenem and vancomycin were started due to ongoing fever. She was connected to a mechanical ventilator because of respiratory failure due to aspiration pneumonia. She later died due to aspiration pneumonia. Cephoperazone-sulbactam may lead to coagulopathy by affecting the metabolism of vitamin K. Clinicians should therefore be careful if they use this drug.