DNA methylation is an enzyme-driven epigenetic modification that must be precisely regulated to maintain cellular homeostasis. Aberrant methylation status, especially hypermethylation of the promoter sites of tumor-suppressor genes, is observed in human malignancies and is a proven target for cancer therapy. The first-generation DNA demethylating agents, azacitidine and decitabine, are widely used for treating several hematological malignancies. In addition, orally bioavailable prodrugs of azacitidine and decitabine have recently been approved by the FDA. We have developed a silylated derivative of decitabine, OR-2100, which is resistant to degradation by cytidine deaminase and orally bioavailable. It has efficacy against several human hematological malignancies in xenograft mouse models with less hematotoxicity than decitabine. Since DNA demethylating agents are combined with molecularly targeted drugs in clinical use and trials, we think that the less hematotoxic profile of OR-2100 makes it suitable for use as a combination therapy. In this article, we review the therapeutic approach in hematological malignancies with the DNA demethylating agent OR-2100.