Epigenetic regulation is essential to the well-being of developing as well as developed cells by providing tissue-specific gene expression. DNA methylation on cytosine nucleotides is one of the core elements of epigenetic machinery, and stable DNA methylation patterns are maintained by properly regulated DNA methylation and DNA demethylation. DNA methylation has been studied extensively in the past 15 years, while the DNA demethylation process has largely been unknown. In this review, we briefly survey recent advances on DNA methylation/demethylation axis with special emphasis on the aspects of DNA demethylation.