We describe an ovarian mucinous cystadenocarcinoma with a sarcoma-like mural nodule. In the literature, rare cases of ovarian mucinous tumors have been described which contain foci of undifferentiated carcinoma, sarcoma, and sarcoma-like nodules. The distinction between these lesions is important because of poorer prognosis of true sarcoma and anaplastic carcinoma than sarcoma-like mural nodules. This case shows different results of immunohistochemical stain for anaplastic carcinoma.