Sickle cell disease (SCD) is a hereditary disorder caused by β-globin gene mutations. Because 300,000 babies are born with pathogenic mutations in the β-globin gene every year in the world, the development of therapeutic drugs for SCD is an urgent issue. Induction of fetal hemoglobin (HbF) by reactivation of fetal γ-globin gene in erythroid cells, which is suppressed after birth, has been well established as a therapeutic strategy for SCD. Recently, epigenetic modulators, including histone methyltransferase G9a inhibitors, have been proposed as therapeutic agents. In this study, we conducted a high-throughput screening to explore a G9a inhibitor from a chemical library. Through a compound optimization study based on the structural information of the X-ray co-crystal structure of the hit compound and G9a complex, we succeeded in developing a specific and potent G9a inhibitor RK-701. RK-701 treatment induced fetal globin expression both in human erythroid cells and in mice without noticeable toxicity. In this presentation, we will introduce the potential of the novel G9a inhibitor RK-701 as a therapeutic agent for SCD. In addition, we would like to introduce the regulatory mechanism of fetal γ-globin gene expression by G9a, which is clarified by using RK-701.