Ovarian metastasis from lung cancer is very rare, which might lead to a misdiagnosis as primary ovarian cancer. We report a 49-year-old woman presenting to our hospital because of a painful mass in the lower abdomen, with no respiratory symptoms. Her initial diagnosis was stage IVB ovarian cancer with pulmonary metastasis. Therefore, the patient underwent neo-adjuvant Paclitaxel - Carbolatin chemotherapy followed by interval debulking surgery. However, postoperative histopathology and immunohistochemistry findings confirmed the diagnosis of primary lung cancer with ovarian metastases. EGFR exon 19 deletion mutation was found by tumor analysis. Therefore, she was then treated with erlotinib and the disease achieved the partial response and remained stable for 7 months. Diagnosis of lung cancer in the context of ovarian and peritoneal metastases can be difficult. In this circumstance, thorough systemic assessment and immunohistochemistry are essential to confirm the primary.