We reported a case of multiple myeloma, who suffered from the acute myelomonocytic leukemia (AML-M4) after the chemotherapy of alkylating agent. The patient had a history of multiple myeloma and was treated with the regimen of including L-Sarcolysinum and cyclophosphamide for 5 years. The multiple myeloma of this patient was proved to have got the remission through bone marrow aspiration, immunofixation electrophoresis of serum, serum protein electrophoresis and detection of urine light chain. However, a pancytopenia of unknown cause was verified to peripheral blood. During the course of supportive treatment only with blood cell and platelet transfusion, WBC count of this patient showed a rising trend and the blast cells (8%-15%) started to occur in the peripheral blood. The further examination discovered that the ratio of blast cell was beyond 30% in bone marrow smear, and the flow cytometry detected the CD45, HLA-DR, CD13, CD33, CD64 to have the positive expressions. Thus, the diagnosis of multiple myeloma in remission and secondary AML-M4 was established. When the chemotherapy regimen to AML was being planned for this patient, she died of massive hemorrhage of gastrointestinal tract due to thrombocytopenia and ineffectiveness.