A 55-year-old female patient was diagnosed with right breast cancer with brain metastasis of 3 cm in size. Neurological examination revealed paralysis in the left upper and lower extremities. Chemotherapy and hormone therapy were performed. Brachytherapy by Cyberknife was performed for the brain metastatic lesion. As a result, the brain metastatic lesion decreased in size to 1 cm on the CT-scan after 2 months. The paralysis disappeared and the patient's QOL improved. Cyberknife therapy was useful for a brain metastatic lesion that harmed the patient's QOL.