EZH2 (Enhancer of zeste homolog 2) is the catalytic subunit of the polycomb repressive complex 2 (PRC2), which is involved in repressing gene expression by methylating lysine 27 of histone H3 (H3K27) and regulates cell proliferation. EZH2 overexpression is implicated in tumorigenesis and has been a candidate oncogene in several tumor types. Recently, point mutations of EZH2 at Tyr641 and Ala677 were identified in diffuse large B cell lymphoma and follicular lymphoma, where they drive H3K27 hypertrimethylation and cancer progression. Here, we reported a novel, highly potent and selective small molecule inhibitor of EZH2, ZLD10A, which inhibited wild-type and mutant versions of EZH2 with nanomolar potency and had greater than 1000-fold selectivity against 10 other histone methyltransferases. Our results have shown that the compound suppressed global H3K27 methylation and cause the anti-proliferation effects in a concentration- and time-dependent manner in DLBCL cell lines. These results demonstrated that ZLD10A, as a novel EZH2 inhibitor, could be a potential promising agent for the treatment of EZH2 mutant lymphoma.