AbstractThe biological roles of epithelial–mesenchymal transition (EMT) in the pathogenesis of radiation‐induced lung injury (RILI) have been widely demonstrated, but the mechanisms involved have been incompletely elucidated. N6‐methyladenosine (m6A) modification, the most abundant reversible methylation modification in eukaryotic mRNAs, plays vital roles in multiple biological processes. Whether and how m6A modification participates in ionizing radiation (IR)‐induced EMT and RILI remain unclear. Here, significantly increased m6A levels upon IR‐induced EMT are detected both in vivo and in vitro. Furthermore, upregulated methyltransferase‐like 3 (METTL3) expression and downregulatedα‐ketoglutarate‐dependent dioxygenase AlkB homolog 5 (ALKBH5) expression are detected. In addition, blocking METTL3‐mediated m6A modification suppresses IR‐induced EMT both in vivo and in vitro. Mechanistically, forkhead box O1 (FOXO1) is identified as a key target of METTL3 by a methylated RNA immunoprecipitation (MeRIP) assay. FOXO1 expression is downregulated by METTL3‐mediated mRNA m6A modification in a YTH‐domain family 2 (YTHDF2)‐dependent manner, which subsequently activates the AKT and ERK signaling pathways. Overall, the present study shows that IR‐responsive METTL3 is involved in IR‐induced EMT, probably by activating the AKT and ERK signaling pathways via YTHDF2‐dependent FOXO1 m6A modification, which may be a novel mechanism involved in the occurrence and development of RILI.