Since ""Reticulum cell sarcoma"" had been named by Oberling in 1928, it has been frequently observed and intensive studies were carried out by many workers. Reticulum cell sarcoma in the ENT fields is a very rare tumor and it is known as a highly malignant tumor histopathologically and clinically. Recent immunological studies suggest that these cells are derived from B-lymphocytes in many instances. We experienced a case of reticulum cell sarcoma in the left maxillary sinus. The patient was an 18 year-old male who had suffered from toothache, left facial swelling and blood-tinged rhinorrhea for the past one year. It was partially removed under the local anesthesia. The clinical and pathological features are also reviewed.