Radiation therapy for malignancy of head and neck leads to secondary effects, such as mucositis, xerostomia, dental caries and osteoradionecrosis. Osteoradionecrosis is a delayed complication which causes chronic pain, infection and constant deformity after necrosis. It occurs spontaneously or after primary oncologic surgery, dental extraction or by trauma of prosthesis. To reduce the incidence of osteoradionecrosis, appropriate antibiotic usage, atraumic procedure, tension-free primary suture and hyperbaric oxygen therapy are essential. This case is about a 74 years old woman who was treated for osteoradionecrosis after extraction of right lower molar at year 2006. She had received radiation therapy for angiosarcoma on tongue at year 2004. At year 2008 the patient came to our hospital for extraction of the opposite premolar but despite careful treatment, osteoradionecrosis occurred again. She was successfully treated by surgical procedure so we report this case.