The prognosis associated with brain metastasis arising from breast cancer is very poor. Eribulin is a microtubule dynamic inhibitor synthesized from halichondrin B, a natural marine product. In a phase III study (EMBRACE), eribulin improved overall survival in patients with heavily pretreated metastatic breast cancers. However, these studies included few patients with brain metastases. Metastatic brain tumors (MBT) were detected during first-line palliative chemotherapy in a 43-year-old woman with breast cancer metastasis to the lung and mediastinal nodes; the genetic subtype was luminal B-like human epidermal growth factor receptor 2 (HER2)-negative. Whole brain radiotherapy (WBRT) followed by eribulin treatment continuously decreased the size, and induced regression, of the MBT with systemic disease stability for 12 months. Another 48-year-old woman with metastatic breast cancer (HER2+ subtype) presented with MBT. Following surgical resection of the tumor, eribulin with concurrent WBRT showed regression of the MBT without systemic progression for 18 months.