Enzymatic oxidative polymerization of m-ethynylphenol possessing two reactive groups, phenol and acetylene moieties, was carried out in aqueous methanol under air. Horseradish peroxidase and hydrogen peroxide were used as catalyst and oxidizing agent, respectively. H-1 NMR and IR analysis showed that only the phenolic moiety was polymerized to produce the polymer having the ethynyl group in the side chain. The reaction of the monomer using a copper/amine catalyst, a conventional catalyst for oxidative coupling, exclusively produced a diacetylene derivative. From these data, it was found that the peroxidase catalysis induced the chemoselective polymerization of the monomer. The resulting polymer was converted to carbonized polymer in a much higher yield than enzymatically synthesized poly(m-cresol) and is expected to have potential applications as a reactive starting polymer.