Sinonasal undifferentiated carcinoma(SNUC) is a distinct, relatively rare neoplasm arising in the nasal cavity and paranasal sinuses composed of undifferentiated epithelial cells and clinically characterized by a fulminant course. We report a case of SNUC in a 56-year old man who have had bilateral neck masses since one month ago before coming to our hospital. The paranasal computed tomography showed soft mass density in the left maxillary sinus and the nasal cavity with bone destruction in the anterior medial and the inferior maxillary sinus wall. This mass was extruded into the left orbital wall. Biopsy of the nasal mass and fine needle aspiration(FNA) of the neck mass were done. FNA revealed medium-sized neoplastic cells forming clusters or individually dispersed. Nuclei were round to oval, slightly to moderately pleomorphic, and hyperchromatic. Chromatin was finely granular, but occasionally was coarsely granular. Nucleoli varied from large to inconspicuous and the cytoplasm was scanty.