Objective: To investigate the clinical and pathological features, diagnosis and differential diagnosis, treatment and prognosis of mixed phenotype acute leukemia. Methods: Retrospective analysis of the clinical data was conducted in one case of mixed phenotype acute leukemia, and the histopathological morphology, immunohistochemistry staining, flow cytometry, karyotype analysis, treatment and follow-up data, and review of the literature. Results: Under light microscope, cervical enlarged lymph node biopsy showed that basic structure of the lymph node was damaged, significant lymphoid follicles and mantle zone couldn’t be seen, and was replaced by small to medium-sized and relatively uniform atypical lymphoid cells. The atypical lymphoid cells showed lesser cytoplasm, round or oval nuclei, the chromatin were uniform, nucleoli were inconspicuous or occasionally could be found, and the mitotic were visible. Immunohistochemically, stains revealed LCA were more scattered positive in the atypical lymphoid cells, they were strong diffused positivity for CD7, TdT and CD10, and were partly positive for MPO. Peripheral blood smear and bone marrow smear all showed primitive naive cells; it was showed acute myeloid leukemia and acute B lymphoblastic leukemia respectively before and after the first time chemotherapy by flow cytometry. Karyotype analysis of short-term bone marrow culture showed deletion of 11q. The above morphology of lymph node biopsy, immunohistochemical staining of lymph noid, peripheral blood and bone marrow smears, bone marrow flow cytometry and karyotype analysis, etc., all these results supported the diagnosis of mixed phenotype acute leukemia (conversion type). Although the patient was given different chemotherapy regimens, it got little effect, he suffered recurrent lung infections and bone marrow suppression, suggested that the prognosis of mixed phenotype acute leukemia (conversion type) was very poor. Conclusion: The incidence of mixed phenotype acute leukemia is very low; generally it requires a combination of morphology, immune phenotype and cytogenetic and other tests to make a final diagnosis, differential diagnosis of the disease, treatment options and prognosis are all important. Therefore, grasp the clinical and pathological features of the disease play an important role in the differential diagnosis, treatment and prognosis of this disease.