We experienced therapy-related acute myeloid leukemia (t-AML) in a patient with extensive disease-small cell lung cancer (ED-SCLC). This case is rare and has educational message because ED-SCLC has a poor prognosis and often cannot survive until developing therapy related hematological malignancy. Furthermore this case had unique chromosomal abnormalities. With recent advances in chemotherapy and radiotherapy, the prognosis of lung cancer has improved, while t-AML has been increasing in frequency.