Therapy-related myelodysplastic syndrome and therapy-related acute myelocytic leukemia (AML) are now recognized as hematologic malignancies that occur a few years after chemotherapy for primary malignancy with alkylating agents or topoisomerase II inhibitors. The secondary leukemia is usually AML and sometimes is preceded by a myelodysplastic syndrome. Acute lymphoblastic leukemia (ALL) as a secondary leukemia is quite rare, and secondary T-cell ALL after AML is even rarer. We report a case of a 56-year-old woman who developed T-cell ALL after a 3-year remission of AML (M2). We thought that this case would be extremely valuable for studying the etiology and biological characteristics of T-cell ALL as a secondary leukemia after AML.