We report a case of myeloid/natural killer cell precursor acute leukemia. A 68-year-old man was diagnosed as having lymphoma in his neck, and was referred to our department for further examination and treatment. After admission, blastoid-cells appeared and increased rapidly in his peripheral blood. Cell marker analysis revealed that the blastoid-cells expressed CD7, CD56, CD33, and CD34. He was then diagnosed with myeloid/natural killer cell precursor leukemia. This form of leukemia was recently established as a distinct disease entity. Further clinicopathological evaluation and the establishment of treatment are necessary.