〔Abstract〕 To investigate the effect and mechanism of methyltransferase-like3 (METTL3) , which func- tions as m6 A modification methyltransferase , on the cellular proliferation , clone formation and migration of non- small cell lung cancer (NSCLC) cells . Methods The METTL3 level and patient overall survival were analyzed by bioinformatics . In the transfected A549 cells , the expression of METTL3 was detected by RT-PCR and Western blot assays , the m6 A level was detected by m6 A RNA Methylation Assay kit , the cellular viability and growth were de- tected by CCK8 assay , the apoptosis was detected by immunofluorescent assay , the colony growth was detected by clone formation assay , the cell migration growth was detected by scratch . Results Bioinformatics showed that METTL3 was highly expressed in NSCLC and negatively correlated with patient overall survival . The RT-PCR and Western blot data showed that the METTL3 level was higher in NSCLC cells . Moreover , higher METTL3 signifi- cantly promoted m6 A level , cell proliferation , colony formation , migration , inhibited cell apoptosis , increased the mRNA and protein expressions of EMT-related marker Vimentin but inhibited apoptosis and decreased the mRNA and protein expressions of EMT-related marker E-cadherin in the A549 cells . Furthermore , the contrasting results were obtained in the A549 cells with the knockdown of METTL3 . Conclusion The over-expressed METTL3 in- creases the m6 A levels in NSCLC cells and promotes cellular proliferation , colony formation , and migration growth , thereby laying a theoretical foundation for future research on early diagnosis and targeted drug development for NSCLC by targeting METTL3 .