Abstract: Methyltransferase is an important metabolic enzyme whose main function is to catalyze the methylation of nitrogen, oxygen and sulfur atoms. It plays an important role in the metabolism of exogenous and exogenous compounds, including drugs in vivo. Methyltransferases are widely distributed in different tissues, with the liver and kidneys being the most abundant. In addition, the structure and activity of the enzyme have certain species and individual differences. This article will describe the biological properties of methyltransferases and their role in drug metabolism.