Histone deacetylases (HDACs; EC 3.5.1.98) are a class of enzymes that remove acetyl groups from an ε-N-acetyl lysine amino acid of histones. Inhibitors of this class of enzymes have a long history of use in psychiatry and neurology as mood stabilizers and anti-epileptics. Moreover, Histone deacetylase inhibitors (HDIs) are being studied as an alleviator or treatment for neurodegenerative diseases[1]. Recently, this class of enzymes is emerging as an exciting new class of potential anticancer agents for the treatment of solid and hematological malignancies[2] by inhibiting the proliferation and induction of differentiation and/or apoptosis of tumor cells in culture and in animal models[3]. HDAC inhibition causes acetylated nuclear histones to accumulate in both tumor and normal tissues, providing a surrogate marker for the biological activity of HDAC inhibitors in vivo[4]. HDAC inhibition not only results in acetylation of histones but also transcription factors such as p53, GATA-1 and estrogen receptor-alpha. The functional significance of acetylation of non-histone proteins and the precise mechanisms whereby HDAC inhibitors induce tumor cell growth arrest, differentiation and/or apoptosis are currently the focus of intensive research. Several HDAC inhibitors have shown impressive antitumor activity in vivo with remarkably little toxicity in preclinical studies.