The malignant transformation rate of ovarian mature teratomas is <1%, and adenocarcinomas account for approximately 7% of these malignant transformation cases. Mucinous carcinomas account for most adenocarcinomas; however, adenocarcinomas with intestinal differentiation(intestinal adenocarcinomas) are less common. Here, we report a case of intestinal adenocarcinoma considered to be caused by the malignant transformation of a teratoma with benign goiter morphology, which was immunohistochemically positive for the special AT-rich sequence-binding protein-2 (SATB2) that is specifically expressed in the colon. An 80-year-old woman consulted with her previous physician owing to a sensation of abdominal distension. Ultrasound revealed an ovarian enlargement that led her to consult our department. Magnetic resonance imaging revealed a cystic lesion that was 20 cm long, with contrast enhancement and diffusion limitation. Imaging revealed no evidence of metastasis to other organs such as the lymph nodes or peritoneum. Furthermore, there were no significant lesions in the gastrointestinal tract. However, serum carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9, and CA125 levels were all elevated, suggesting ovarian cancer. Biopsy of the cervix revealed clear-cell carcinoma, suggesting simultaneous duplication of cervical and ovarian cancer or metastasis of ovarian cancer to the cervix. Because of the patient’s low activities of daily living score, modified radical hysterectomy, bilateral adnexectomy, and omentectomy were performed. Intraoperative rapid ascitic fluid cytology was negative, and there was no evidence of metastases to the lymph nodes or peritoneum. The final pathological diagnosis was a complication of cervical clear-cell carcinoma in situ (pT1b1NxM0) with intestinal adenocarcinoma and goiter carcinoid tumor (pT1aNxM0) of the ovary. The patient is currently being followed up without additional treatment. Because of the presence of an intestinal adenocarcinoma, we considered the case to be a malignant transformation of the primary teratoma of the left ovary. The intestinal adenocarcinoma was identified as a colorectal-type intestinal adenocarcinoma because immunohistochemical analysis showed that it was negative for cytokeratin (CK) 7 but positive for CK20, caudal type homeobox 2, and SATB2. Thirteen cases of intestinal adenocarcinoma have been previously reported, all of which were derived from teratomas, and the present case was considered to be similar to the previous cases. SATB2 staining was not performed in any of the previously reported cases, which made our case report. [Adv Obstet Gynecol, 74(1) : 171-178, 2022 (R4.2)]