Metastasis is the major cause of treatment failure in anaplastic thyroid carcinoma (ATC) patients. In the preliminary study, we demonstrated that interleukin (IL)-11 expression is positively correlated with distant metastasis in ATC. However, the mechanisms underlying remain largely unknown. Here, we found that cobalt chloride (a hypoxia mimetic) promoted IL-11 expression via HIF-1 alpha activation. Furthermore, the resultant increase in IL-11 expression significantly induced epithelial-mesenchymal transition (EMT) in ATC cells, accompanied by Akt/GSK3 beta pathway activation and increased invasive and migratory abilities. Conversely, HIF-1 alpha or IL-11 knockdown, or treating cells with a neutralizing antibody against IL-11, a PI3K inhibitor, or Akt inhibitor V, significantly suppressed the induction of EMT and counteracted the enhancements in invasive and migratory abilities. These results indicate that hypoxia increases IL-11 secretion in ATC cells via HIF-1 alpha induction and that IL-11 then induces EMT in these cells via the PI3K/Akt/GSK3 beta pathway, ultimately improving their invasive and migratory potential. This study elucidates the prometastatic role played by IL-11 in ATC metastasis and indicates it as a potential target for the treatment of cancer metastasis. However, many questions remain to be explored.