A patient with diffuse, well-differentiated malignant lymphoma later developed acute nonlymphocytic leukemia(ANLL) 9 months following the diagnosis. The patient received radiotherapy and long term courses of alkylating agent therapy for the malignant lymphoma. Malignant lymphoma at the diagnosis of leukemia relapsed and developed in generalized lymph nodes, liver and spleen. The ANLL was signalled by increasing anemia and thrombocytopenia. With an intensive chemotherapy for the ANLL, however, the survival from the leukemia was one month. A case of ANLL developing after radiotherapy and chemotherapy for a well differentiated malignant lymphoma were discussed with brief current literature review.