METTL3 is a crucial member of the methyltransferase family, primarily responsible for N6-methyladenosine (m6A) modification of RNA. It forms a core complex with METTL14, participating in the establishment of m6A. Located predominantly in the cell nucleus, METTL3 regulates RNA metabolism, stability, and translation, influencing cell differentiation, development, and responses. METTL3 is expressed in various cells and tissues, and changes in its expression levels and activity are closely associated with diseases such as cancer and neurodevelopmental disorders. Regulation of specific gene expression and mutations can affect m6A modification patterns, thereby influencing gene expression and cellular functions, highlighting its crucial role in biological processes and disease development.