Objectives: Recently, N6-methyladenosine (m6A) RNA methylation has been reported to participate in post-transcriptional gene expression regulation and development of kidney fibrosis. We aimed to investigate the effect of RNA methylation signaling pathway inhibition mediated by METTL3 on kidney fibrosis. Methods: We evaluated the expression of m6A RNA methyltransferases (e.g., METTL3, METTL14, WTAP), demethylases (e.g., FTO and ALKBH5) and reader proteins (YTHDF1-3) in unilateral ureteral obstruction (UUO) model. Furthermore, we incubated human proximal tubular epithelial (HK2) cells under TGFβ treatment as an in vitro model of kidney fibrosis. STM2457 is a highly potent and selective first-in-class catalytic inhibitor of RNA methyltransferase METTL3. Effects of RNA methylation signaling pathway inhibition by STM2457 in vivo mice UUO model (2 weeks) and in vitro TGFβ (10 ng/ml) challenged HK2 cell model were explored.   Results: In HK2 cell, m6A RNA methyltransferases (METTL3 and METTL14) and reader protein (YTDHF1) expression increased in dose- and time-dependent manner along with N-cadherin expression by the TGFβ treatment. Also, cellular levels of m6A in both total RNA and mRNA were significantly elevated by the TGFβ treatment. In the UUO model, METTL3 expression and m6A levels in RNAs were significantly increased. Down-regulation of METTL3 in HK2 cell decreased the expression of TGFβ-induced fibrosis maker such as alpha smooth muscle actin and fibronectin. Inhibition of METTL3 attenuated the degrees of kidney fibrosis in vivo mice UUO model (areas of fibrosis 5.5% ± 2.4% in UUO/vehicle vs. 1.6% ± 0.8% in UUO/STM2457, P = 0.003) Conclusions: Inhibition of RNA methylation signaling mediated by METTL3 attenuates kidney fibrosis both in vitro TGFβ-challenged HK2 cell model and in vivo mice UUO model. Modification of RNA methylation signaling pathway could be a new target for treatment of kidney fibrosis.