SNUC (undifferentiated sinonasal carcinoma) is a rare tumor. The exact cause of this cancer is not known. Patients usually have signs and symptoms of bleeding from the nose, runny nose, duplicate photos, symptoms of chronic sinus infections and nose, nasal obstruction, or facial pain. We reported a case of seventy year old patient with sinonasal undifferentiated carcinoma in the right maxillary sinus. Six months ago, the patient was conducted operations polyp in the right nasal hall. He had pain in the right side of his face and swelling in the mouth in the area of the upper jaw on the right side. The patient was operated tumor of the right maxillary sinus, with expansion in the ethmoid sinus, nasal cavity and infratemporal space. The neck dissection was done on the same side. Postoperatively, he received radiation therapy and chemotherapy. SNUC is very rare aggressive cancer that requires aggressive therapy. This cancer is considered in need of modified maxillary sinuses, as well as for modified sinus in polyps or after the operation of the same. Despite extensive surgery, radio therapy and implemented chemotherapy, the prognosis of these tumors is very poor.