Malignant transformation of mature cystic teratoma (MCT) is a rare phenomenon with incidence of approximately 1-3%. We report a 48-year-old woman who presented to the emergency room with symptoms of bowel obstruction. She underwent computed tomography scan for the evaluation of obstruction, which demonstrated diffuse ascites accompanying a cystic pelvic to lower abdominal mass which had invaded into the adjacent small bowel causing partial small bowel obstruction. Histologically, the mass demonstrated a MCT within which aroused a well-differentiated squamous cell carcinoma. Exploratory laparotomy was performed to confirm the diagnosis and debulking of the mass was performed.