A few previous reports of severe reactions after carbon ion radiotherapy have been made. Herein, a case of nasal melanoma with various adverse effects after carbon ion radiotherapy is reported. The patient was a 70-year-old man with epistaxis and left nasal congestion. A white mass was found in the right nasal cavity over the nasal septum arising from the left nasal cavity. The histological diagnosis was malignant melanoma of the left nasal cavity. Magnetic resonance imaging revealed that the tumor protruded through the left nasal cavity and into the epipharynx. The enhanced mass showed a mild high signal intensity on T1-weighted images and a mild low signal intensity on T2-weighted images. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) showed a high uptake by the mass from the posterior nasal cavity to the pharynx, and the uptake included the left maxilla. High uptake was also noted in the left subaural and submental regions. The patient underwent carbon ion radiotherapy at the Hyogo Ion Beam Medical Center (Hyogo, Japan). The patient was treated with 60.8GyE/16 fractions to the primary lesion and 56 GyE/8 fractions to the left cervical lymph node metastasis. A complete response was achieved for the primary lesion, while a partial response was achieved in the left cervical lymph node. Thereafter, various acute and late reactions (oral mucosal ulcer, epistaxis, sinusitis, orbital abscess) developed because of necrosis at the radiation site.