Tubo-ovarian abscess caused by Morganella morganii is unusual. A 54-year-old menopausal woman visited the emergency room with lower abdominal pain, vomiting, and fever for 4 days. Pelvic examination revealed lifting tenderness over the right adnexum without motion tenderness of the uterus. Pelvic sonogram revealed a cystic lesion with heterogeneous content in the right ovary. Salpingo-oophoritis was suspected. Clindamycin and gentamicin were administered intravenously after obtaining blood cultures. Laparoscopy was done because of sustained fever, and an ovarian abscess was found. Laparoscopic salpingo-oophorectomy was performed. The patient was discharged 5 days later and oral clindamycin was prescribed. However, she was readmitted due to intermittent fever. The result of blood culture obtained before surgery disclosed M. morganii, which was resistant to clindamycin and cefazolin. Her symptoms resolved after administration of intravenous flomoxef. This report highlights the fact that antimicrobial resistance of M. morganii may complicate the management and outcome of this infection.