Immature-type CD56+ natural killer (NK)-cell neoplasms are classified as either myeloid/NK-cell precursor acute leukemia or blastic NK-cell lymphoma. We identified two cases of immature-type CD56+ NK-cell neoplasms that were not categorizable as either of these entities. The first case involved a 74-year-old woman presenting with skin eruptions and pancytopenia due to bone marrow necrosis. Skin biopsy specimen revealed CD4+, CD7−, CD34−, CD43+, CD56+, CD68+, muramidase (lysozyme)+, and myeloperoxidase (MPO)−, and immunophenotyping of peripheral blood showed CD4+, CD7−, CD13+, CD33+, CD34−, CD43+, CD56+, cytoplasmic (cy)CD68+, CD123+, and HLA-DR+. The second case involved a 62-year-old man who had bilateral optic nerve tumor and presented with malignant cells in peripheral blood. Cell surface markers of malignant cells showed CD4+, CD7−, CD13+, CD33+, CD34−, CD43+, CD56+, cyCD68+, and HLA-DR+. The phenotypes of tumor cells in both cases were compatible with blastic NK-cell lymphoma, except for the expression of myeloid antigen. Clinical presentations of these cases showed characteristics of both blastic NK-cell lymphoma and myeloid/NK-cell precursor acute leukemia.