Carbon ion radiotherapy, a form of charged particle radiotherapy that has been used to treat various inoperable and radio-resistant tumors, has been associated with less severe late effects than conventional radiotherapy. A 63-year-old woman with a soft palate defect received carbon ion radiotherapy (total dose: 64 Gray equivalents). Several late effects were observed, and osteoradionecrosis was observed not only on the tumor side but also on the other side and gradually expanded during maxillofacial prosthetic rehabilitation. While the definitive prosthesis improved her speech and eating ability, careful adjustments and close follow-up should continue with respect to postradiation effects.