Butyrylation of lysine, or the addition of a butyryl group (C4H7O2-) to the ε-amino group of lysine, is a post-translational modification that alters the chemical properties of lysine and potentially impacts the structure and function of proteins. Lysine butyrylation is a relatively new acetylation-like modification that has been found and reported in various biological processes, including energy metabolism, tumor development, and DNA damage repair.