Disclosed is a synthesis method for synthesizing in a short time and selectively a microcrystal of a polymer complex having three three-dimensionally and regularly arranged channels.Specifically disclosed is a synthesis method of a polymer complex crystal wherein (1) a metallic solution, which is a mixture of zinc halide(II) and a solvent A that can dissolve the zinc halide, is mixed with (2) a ligand solution, which is a mixture of a tridentate ligand that has three coordination sites coordinated to zinc of the zinc halide and a solvent B that can dissolve the tridentate ligand, to be a single-phase solution, thereby synthesizing a microcrystal of a polymer complex having a three-dimensional coordination network formed by coordinating the tridentate ligand to the zinc and having channels that are three-dimensionally and regularly arranged in the three-dimensional coordination network.