Epigenetics is a cell intrinsic mechanism to maintain genomic integrity by modifying chromatin architecture independently of changes in heritable DNA sequences namely genetic code. Chromatin is composed of nucleosome cores, in which DNA(147bp) is wrapped around a core histone octamer(two each of histones H2A, H2B, H3 and H4), arranged in a "beads-on-a-string array" with linker histones and non-histone nuclear proteins. The chromatin structure could be altered by chemical modifications of DNA and histones, including methylation and acetylation, without affecting genetic codes. In mammals, DNA methylation is mediated via DNA methyltransferases (Dnmt) at CpG dinucleotides. Histones are modified by numerous enzymes, such as histone acetyltransferases (HATs), deacetylases (HDACs), methyltransferases and demethylases, in spatio-temporarily distinct manners. These modifications could alter chromatin structures to regulate a wide variety of biological processes such as gene expression, cell cycle progression and DNA repair. Given the biological importance of epigenetic modifications, it is easy to speculate that the abnormalities of chromatin modifying enzymes and reader proteins underlie several human diseases such as cancer, inflammation and metabolic disorders. Because epigenetic states are reversible and could be modified in response to extrinsic signals, including small molecular compounds, an increased understanding of their molecular framework would allow us to treat pathological conditions caused by epigenetic alterations. Indeed, Dnmt inhibitors and HDAC inhibitors have already applied to the treatment of hematological malignancies with considerable success.