DNA methylation and posttranslational histone modifications regulate expression of various genes independently of changes in the DNA sequence. Such epigenetic mechanisms play important roles in controlling cellular functions, including the cell cycle, immunoresponses and signal transduction. On the other hand, epigenetic aberrations are associated with oncogenesis and proliferation of cancer cells, and epigenetic alterations have been identified in many human cancer cells. Furthermore, chemical–biological approaches have uncovered relationships between epigenetic dysregulation and cancer, and several small molecules that modulate epigenetic mechanisms have already been approved for cancer therapy. In this review, we deal with chemical epigenetics relevant to cancer therapy, focusing especially on small molecules that regulate epigenetic mechanisms related to DNA methylation and histone modification.