An efficient method for attachment of a variety of reporter groups to oligonucleotides (ONs) is copper (I) [Cu(I)]-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition ("click reaction"). However, in the case of ONs with phosphorothioate modifications as internucleosidic linkages (PS-ONs), this conjugation method has to be adjusted to be compatible with the sulfur-containing groups. The method described here is adapted for PS-ONs, utilizes solid-supported ONs, and implements the Cu(I) bromide dimethyl sulfide complex (CuBr × Me2 S) as a mediator for the click reaction. The solid-supported ONs can be readily transformed into "clickable ONs" by on-line addition of an alkyne-containing linker that subsequently can react with an azido-containing moiety (e.g., a peptide) in the presence of CuBr × Me2 S. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Conjugation on solid support Support Protocol: Removal of 4,4'-dimethoxytrityl group from amino linker Basic Protocol 2: Removal of protecting groups and cleavage from solid support Basic Protocol 3: HPLC purification.