Native chemical ligation (NCL) allows the chemical synthesis of proteins and peptides with excellent efficiency, starting from a mixture of unprotected short peptide fragments. The chemo and regioselectivity of NCL provide access to functional biomacromolecules such as peptides without protection-deprotection strategies under mild conditions. In contrast, less progress has been made in non-natural polymer conjugation. Metal contamination, synthetic difficulties, laborious purifications or lack of functional group tolerance limit complex functional polymer design. Here, we have studied the potential of NCL for non-natural polymer conjugation. Diblock and ABA triblock copolymers were synthesized via NCL with high efficiency within one hour at room temperature. An A-alt-B block copolymer was also synthesized with a re- markable degree of polymerization from bifunctional thioester and cysteine end functional polymers. The SEC and NMR spectroscopy analyses of the synthesized polymers confirmed the block structure of the polymers and the excellent efficiency of NCL for non-natural polymer conju- gation.