N6-methyladenosine (m6A) is the most prevalent modification of eukaryotic RNA, which is recognized by m6A-binding proteins (“readers”) and thereby mediates multiple biological processes. Dysregulation of the m6A readers has been linked to various pathologies, but the therapeutic potential of small molecule inhibitors targeting the m6A readers is unknown. Here we report the identification and characterization of a highly potent and selective first-in-class inhibitor (YL-5092) of YT521-B homology (YTH) domain-containing protein 1 (YTHDC1), which is a nuclear RNA m6A reader and plays essential roles in the pathological process of acute myeloid leukemia (AML). The crystal structure of YTHDC1 in complex with YL-5092 well explained its potency and selectivity. YL-5092 treatment substantially suppressed the proliferation and induced the differentiation and apoptosis of AML cells. It also efficiently inhibited the colony-forming ability of CD34+ AML stem cells, but had no effect on normal hematopoietic stem cells and early progenitors (Lin− Sca1+ Kit+). Moreover, YL-5092 treatment impaired leukemogenesis and improved the animal survival rate in mouse AML xenograft models. Collectively, this research reveals a therapeutic potential of YTHDC1 inhibitors against AML, and provides proof of concept that targeting m6A readers represents a promising strategy for cancer treatment.