Development of malignant tumors is related to epigenetic changes caused by abnormal methylation of DNA. Therefore, the demethylation treatment represented by decitabine has been gradually playing an important role in the field of tumor therapy in recent years. This article reviews the clinical use of decitabine in myelodysplastic syndromes, acute myeloid leukemia, juvenile myelomonocytic leukemia and other hematological malignancies, and provides evidences for optimal dosage and safety of this drug.