Uterine carcinosarcoma (termed malignant mixed müllerian tumor) is a rare neoplasm of the uterus with a poor prognosis. There have been very few cases in the literature describing the PET/CT findings of uterine carcinosarcoma. We report a case of tissue-proven carcinosarcoma of the uterine corpus in a 65-year-old woman with elevated serum alpha-fetoprotein (AFP), whose 18F-FDG PET/CT showed a 10.3-cm mass in the uterus with uneven high FDG uptake. The SUVmax was 12.8. After surgery, the patient received 6 courses of chemotherapy, and the serum levels of AFP decreased to reference range.