The purpose of this study is to present a case of secondary dementia caused by diffuse axonal injury. We diagnosed this patient with diffuse axonal injury by using brain computerized tomography(CT) and magnetic resonance imaging(MRI), and also diagnosed secondary dementia based on DSM-IV. To evaluate prognosis of the patient, we used K-DRS(Korean-Dementia Rating Scale) and gave him a written test. As a result of treating this patient with oriental medicine, the K-DRS score increased and the overall clinical symptoms improved. In oriental medicine, case studies of diffuse axonal injury are yet insufficient, hence more clinical studies and researches will be needed.