Exendin-4 is an agonist of the glucagon-like peptide 1 receptor (GLP-1R) and is used in the treatment of type 2 diabetes. Since human GLP-1R has been identified in various cells besides pancreatic cells, exendin-4 is expected to exert extrapancreatic actions. It has also been suggested to affect gene expression through epigenetic regulation, such as DNA methylation and/or histone modifications. Furthermore, the expression of extracellular-superoxide dismutase (EC-SOD), a major SOD isozyme that is crucially involved in redox homeostasis, is regulated by epigenetic factors. In the present study, we demonstrated that exendin-4 induced the demethylation of DNA in A549 cells, which, in turn, affected the expression of EC-SOD. Our results showed that the treatment with exendin-4 up-regulated the expression of EC-SOD through GLP-1R and demethylated some methyl-CpG sites (methylated cytosine at 5'-CG-3') in the EC-SOD gene. Moreover, the treatment with exendin-4 inactivated DNA methyltransferases (DNMTs), but did not change their expression levels. In conclusion, the results of the present study demonstrated for the first time that exendin-4 regulated the expression of EC-SOD by reducing the activity of DNMTs and demethylation of DNA within the EC-SOD promoter region in A549 cells.