Skull base osteoradionecrosis(ORN)is a rare complication of radiotherapy for nasopharyngeal carcinoma, but is one of the most severe and possibly fatal condition followed by radiotherapy. However, the treatment of skull base ORN has seldom been thoroughly described yet. Here we report a case of skull base ORN that was successfully treated with hyperbaric oxygen therapy(HBO). A 52-year-old man visited our department complaining of trismus and foul odor. He was diagnosed with nasopharyngeal cancer with multiple lymph node metastasis one year ago and underwent concurrent chemoradiotherapy. On the physical examination, mucopus and crusts with exposed necrotic bone was seen in the right nasopharynx. On the paranasal sinus magnetic resonance imaging, osteoradionecrosis which was extending from the right nasopharynx to the clivus, petrous apex, and cavernous sinus was noted. Nasopharynx biopsy resulted of ulcer with no malignant cells. HBO therapy was performed with debridement of nasopharynx for 3 months. There was no sign of recurrence or residual ORN 18 months after HBO therapy.