My thesis is about histone deactylase inhibitor which inhibit acetylation in lysine residues of core histones. HDAC inhibitor involved in cell proliferation and death, altering their function. HDACIs have been studied for their potential therapeutic use in various diseases, including cancer, neurodegerative disease, and inflammatory disorder. Their is several drugs for example vorinostat, valproic acid, trichostatin A etc. HDACI have limitation which is lack of specificity, potential to induce resistance, and limited efficacy in certain tumor types. HDACIs have shown promise in preclinical and clinical studies for the treatment of various diseases, further research is needed to fully understand their pharmacological properties and potential therapeutic uses.