〔Abstract〕 Objective To explore the molecular mechanism of N6-methyladenosine(m6A) methylation mediated by methyltransferase 3(METTL3) in regulating lipopolysaccharide(LPS)-induced endothelial cell permeability changes. Methods Human umbilical vein endothelial cells(HUVECs) were culturedin vitro. HUVECs were treated with LPS 50, 125, 250, 500, 1 000, 2 000 ng/ml for 24 h. METTL3 mRNA expression was detected by Real-time PCR. After HUVECs were intervened with 500 ng/ml for 24 h, the methylation level of m6A was detected, and cell permeability was measured by cell permeability test. Real-time PCR and Western blot were used to detect mRNA and protein expression of intercellular junction proteins(Claudin-5, Occludin and VE-caherin). METTL3 overexpressed stable cell lines were constructed to measure the changes of m6A methylation level and permeability of endothelial cells during METTL3 overexpression. Results Compared to the control group, LPS inhibited the expression of HUVECs METTL3 mRNA, decreased the methylation of m6A, increased the cell permeability, and decreased the mRNA and protein expression of intercellular junction proteins(Claudin-5, Occludin and VE-Caherin). When METTL3 was overexpressed, the m6A methylation levels of endothelial cells were enhanced, and the increase of endothelial cell permeability induced by LPS was reversed. Conclusion METTL3-mediated m6A methylation can improve the permeability of endothelial cells induced by sepsis.