Ameloblastoma is an epithelial origin, nonfunctional neoplasm. The patients are equal in gender and reported to have mean age between 30 to 40 years old. The clinical manifestations of this tumor are generally painless without obvious symptoms or signs. The disease is tentatively diagnosed by imaging study, and is confirmed histologically. The main treatment for ameloblastoma is tumor resection with or without reconstruction surgery. The optimal treatment options for clinically inoperable disease or refusal of operation are not defined. Radiotherapy is able to increase the likelihood of local control. The 50-year-old patient visited our hospital due to painless mass over his anterior mandible. Histologic examination showed ameloblastoma. The patient refused operation. Radiotherpy with 60 Gy in 30 fractions by three-dimensional conformal radiation therapy (3D-CRT) was delivered. After 6-year follow-up, there was no local recurrence.