Obstructive sleep apnea (OSA) is closely associated with cancer progression and cancer-related mortality. N6-methyladenosine (m(6)A) is involved in the process of intermittent hypoxia (IH) promoting tumor progression. However, it is unclear how m(6)A regulates the development of lung adenocarcinoma under IH. In this study, we found that ALKBH5 was elevated in lung adenocarcinoma cells and subcutaneous tumors in mice under IH, which was associated with decreased m(6)A levels in these cells and tissues. Next, we knocked out ALKBH5 in a human lung adenocarcinoma cell line under IH, and we found that the proliferation and invasion of these cells were significantly inhibited. Mechanistic analysis showed that under IH, knockout of ALKBH5 in lung adenocarcinoma cells upregulated the level of m(6)A in Forkhead box M1 (FOXM1) mRNA and decreased the translation efficiency of FOXM1 mRNA, resulting in down-regulation of the FOXM1 protein. The FOXM1 protein is elevated in lung adenocarcinoma cells and subcutaneous tumor tissues of mice under IH. By knocking out FOXM1 in lung adenocarcinoma cells under IH, proliferation and invasion of these cells were inhibited, and overexpression of FOXM1 partially restored the inhibition of growth and invasion of lung adenocarcinoma cells due to ALKBH5 knockout. Collectively, our findings demonstrate that the m(6)A demethylase ALKBH5 affects the proliferation and invasion of lung adenocarcinoma cells under IH by downregulating m(6)A modification on FOXM1 mRNA and by promoting FOXM1 expression. (C) 2019 Elsevier Inc. All rights reserved.