BCDIN3D is a member of the methyltransferase superfamily and contains 1 Bin3-type SAM domain. BCDIN3D acts in the catalysis of the transfer of a methyl group to an acceptor molecule. BCDIN3D is an O-methyltransferase which specifically dimethylates the 5’ monophosphate of pre-miRNAs, serving as a negative regulator of miRNA processing. BCDIN3D mediates the methylation of pre-miR-145, as well as other pre-miRNAs.