Abstract: Objective To analyze the diagnostic process of a rare case diagnosed of myeloid／nature killer cell precursor acute leukemia（M／NKPAL）and to improve the recognition of M／NKPAL. Methods Cell morphology was analyzed by marrow smear and related cell chemical staining. Immunophenotyping of blast cells was performed by flow cytometry. Cytogenetics technique was used for karyotype analysis. PCR was applied for detection of T-cell recepter gene rearrangement or fusion gene associated with leukemia. The related articles were reviewed. Results With regard to morphology， most of leukemic cells demonstrated that 90.4％ blasts in the bone marrow were generally L2-shaped with negative reactivity of myeloperoxidase staining and Auer’s rods were occasionally found. Expression of CD34， HLA-DR，CD33，CD7，CD56，CD38 and cyCD3（dim），but no other markers including cyMPO，CD3 and CD4 were observed. Cytogenetics examination revealed abnormal karyotype. Clonal T-cell recepter gene rearrangement and fusion gene were not detected.Conclusion M／NKPAL is considered extremely rare and diagnosis is difficult depending merely on the morphology. It is important to be distinguished from T-cell acute lymphoblastic leukemia with expression of myeloid-antigen， acute myeloid leukemia with minimal differentiation， mixed-phenotype acute leukemia with T／myeloid lineage and blastic NK cell leukemia／lymphoma.