Sorafenib is an emerging therapeutic option for radioactive iodine (RAI)-refractory differentiated thyroid carcinoma. However, the effects of sorafenib as an adjuvant treatment following surgery or radiation on brain metastases from poorly differentiated thyroid carcinoma (PDTC) have never been reported. A 52-year-old patient underwent total thyroidectomy for follicular thyroid carcinoma. Despite high-dose RAI therapy, a neck mass and lung metastases were developed. PDTC was diagnosed by neck mass removal. During adjuvant external beam radiation therapy (EBRT) to the neck, brain metastases developed. After palliative EBRT for brain metastases, the brain tumor size decreased but lung metastases markedly progressed. Off-label sorafenib was used to treat progressive multiple metastatic lesions. Over five months of sorafenib treatment, the sum of the longest diameters for target lesions was decreased by 45% in brain and 13% in lung. Sorafenib can be considered a new adjuvant therapeutic option for metastatic brain lesions from PDTC after EBRT.