Ovarian metastasis (OM) from breast cancer accounts for 3-38% of all ovarian neoplasms and is associated with various characteristic clinical presentations, such as pseudo-Meigs syndrome and Krukenberg tumor. Accurate diagnosis of OM may be challenging, as such lesions are frequently asymptomatic until they reach a large size. Occasionally, metastatic ovarian cancer is detected prior to the diagnosis of the primary tumor. Immunohistochemistry plays an important role in distinguishing primary ovarian tumors from extraovarian tumor metastases and may be helpful for identifying the primary tumor site. We herein report a case of OM from breast cancer masquerading as primary ovarian cancer. However, the correct diagnosis was made based on histopathological and immunohistochemical examinations. The patient had bilateral breast cancer, namely invasive lobular carcinoma of the left breast and ductal carcinoma of the right breast. Due to the presence of bilateral synchronous breast tumors, the possibility that the patient had hereditary breast and ovarian cancer syndrome or other relevant genetic factors was considered. Immunohistochemistry plays a key role in distinguishing between primary ovarian tumors and OM, and it was also important for confirming the metastatic nature of the ovarian lesion and diagnosing the primary tumor in the present study.