A 36-year-old male was admitted to the hospital with anemia and leukopenia. A bone marrow specimen revealed the proliferation of leukemic cells with flower-like nuclei observed in adult T-cell leukemia. The leukemic cells were positive for HLA-DR, CD2, CD7, and CD56. A diagnosis of aggressive NK cell leukemia was made, the patient was treated with induction chemotherapy and cord blood stem cell transplantation, and he is well now. Seen with electron microscopy, some leukemic cells had ribosome-lamella complexes (RLC). This is the first reported case of leukemic cells with flower-like nuclei seen with light microscopy and RLC seen with electron microscopy.