The one-pot combination of enzymatic ring-opening polymerization (eROP) and ring-opening metathesis polymerization (ROMP) is successfully established to construct block copolymers. cis -1,4-Diacetoxy-2-butene is employed both as a precursor to initiate eROP of ε -caprolactone or 15-pentadecanolide and as a chain transfer agent in ROMP. The obtained polymers are systematically characterized by NMR, GPC, DSC, and microTOF-QII MS. An evaluation of the reaction kinetics indicates the presence of two stages during the one-pot eROP/ROMP process. Compared with cascade methods, this one-pot method exhibits many advantages for preparing well-defi ned block copolymers, such as mild reaction conditions and the elimination of complex purifi cation steps for intermediates. Thus, this one-pot combination approach has the potential to be widely used in preparing biocompatible polymeric materials, especially for biological and pharmaceutical applications. chemical methods, the diversity and complexity of macromolecules could be further increased, and chemoenzymatic polymerization could even be utilized to synthesize polymeric materials that are diffi cult to prepare via traditional routes. [ 6,7 ] For example, eROP has been coupled with atom transfer radical polymerization (ATRP), [ 8,9 ] reversible addition-fragmentation chain transfer (RAFT), [ 10 ] and ring-opening metathesis polymerization (ROMP) [ 11,12 ] to prepare polymeric materials.Another issue to be addressed in the modern macromolecular fi eld is improving the synthetic effi ciency and/or minimizing the synthesis and purifi cation steps. To achieve this goal, researchers have combined a series of reactions in a single-step manner to construct complex macromolecules, [13][14][15][16][17][18] especially the combination of living polymerizations and other compatible polymerizations for simple and facile polymer synthesis. [19][20][21][22] The combination of different reactions into a one-pot system could not only avoid separation and purifi cation steps of intermediates, improve chemical yields, and save time and resources, [ 7 ] but also could provide a powerful strategy for sophisticated polymer synthesis and modifi cation. [ 23 ] For instance, based on a successful consecutive polymerization combining eROP and ATRP, [ 24 ]