Oncogenic KRAS mutations combined with the loss of the LKB1 tumor-suppressor gene (KL) are strongly associated with aggressive forms of lung cancer. N6-methyladenosine (m6A) in mRNA is a crucial epigenetic modification that controls cancer self-renewal and progression. However, the regulation and role of m6A modification in this cancer are unclear. We found that decreased m6A levels correlated with the disease progression and poor survival for KL patients. The correlation was mediated by a special increase in ALKBH5 (AlkB family member 5) levels, an m6A demethylase. ALKBH5 gain- or loss-of function could effectively reverse LKB1 regulated cell proliferation, colony formation, and migration of KRAS-mutated lung cancer cells. Mechanistically, LKB1 loss upregulated ALKBH5 expression by DNA hypermethylation of the CTCF-binding motif on the ALKBH5 promoter, which inhibited CTCF binding but enhanced histone modifications, including H3K4me3, H3K9ac, and H3K27ac. This effect could successfully be rescued by LKB1 expression. ALKBH5 demethylation of m6A stabilized oncogenic drivers, such as SOX2, SMAD7, and MYC, through a pathway dependent on YTHDF2, an m6A reader protein. The above findings were confirmed in clinical KRAS-mutated lung cancer patients. We conclude that loss of LKB1 promotes ALKBH5 transcription by a DNA methylation mechanism, reduces m6A modification, and increases the stability of m6A target oncogenes, thus contributing to aggressive phenotypes of KRAS-mutated lung cancer.