We report a case of diffuse large B-cell lymphoma （DLBCL） of the mandible in a super-elderly patient. A 98-year-old man initially presented with pain after a facial blow. Because CT revealed a buccal cortical bone defect of the right-side mandible, a biopsy of the mandibular bone was performed. Hematoxylin and eosin staining showed a diffuse multiplication image of large atypical lymphocytes of medium size; furthermore, immunostaining for the cluster of differentiation CD20, CD79a, and B-cell lymphoma 2 （BCL-2） was positive. In FDG-PET, no site exhibited abnormal accumulation besides the mandibular bone. Therefore, we made a diagnosis of DLBCL of the mandibular bone. Because the patient was super-elderly, the patient and his family declined treatment; thus, best supportive care was provided. However, since the tumor of the mandibular bone grew and the quality of life deteriorated over time, palliative irradiation of 30Gy was performed. As a result, the tumor shrank and survival of 1 year and 8 months was obtained after radiation treatment, but the patient died of another disease.