We report a case of nasal lymphoma with characteristics of natural killer (NH) cells. A 44-year-old man was admitted to our hospital because of right nasal obstruction. Physical examination revealed a tumor in the right nasal cavity and swelling of the right cervical lymph nodes. Histopathological examination showed diffuse medium sized cell lymphoma. The neoplastic cells expressed CD2, NKH-1, HLA-DR and leukocyte common antigen, but lacked other T-cell, B-cell and myeloid markers. They were in germline configuration for immunoglobulin heavy chain and T-cell receptor genes by southern blot analysis. These findings suggest that they are derived from NK cell.