Porous coordination polymers (PCPs), also called metal–organic frameworks (MOFs) for three-dimensional (3D) PCPs, have received much attention due to their potential applications. Currently, nano- and microsized PCPs (nPCPs or mPCPs) have often been reported with their promising applications. They could possess numerous advantages over both the PCPs and inorganic nanomaterials, and their novel and/or enhanced performances are frequently reported with potential applications in catalysis, separation, gas storage, drug delivery, biosensing, and imaging. Although a variety of nPCPs or mPCPs can be successfully obtained by controlling the growth conditions, their fabrication is still a major challenge because of lack of information regarding the crucial factors for the precise control of particles during the synthesis. Furthermore, the translation of building blocks into well-defined structures, whose properties and functions are regulated in the building block level, still remains very challenging. In this regard, metalloporphyrins would be good building blocks for the construction of such functional materials witnessed by a wide range of molecular architectures, such as molecular boxes, self-assembled arrays, and CPs, and MOFs with various applications in catalysis, gas storage, and separation. Particularly, Mn(III)- and Fe(III)-containing metalloporphyrins are often used to fabricate various functional molecular architectures and to mimic the extraordinary behavior of enzymes in both homogeneous and heterogeneous catalysis. In the case of homogeneous catalysis, these materials have frequent trouble with fast catalytic degradation because of µ-oxo dimer formation or ligand oxidation. To avoid the catalyst degradation, the heterogenization of homogeneous catalysts, such as immobilization and site-isolation of homogeneous catalysts on polymers, membranes, and MOF supports, is widely used alternative strategy. Here I like to present the preparation and heterogeneous catalytic uses of Mn(III)–porphyrin that contain size-controlled amorphous and crystalline nano- and microsized CPs. Particularly, I like to focus on the conversion of kinetically controlled amorphous assemblies into thermodynamically controlled crystalline structures based on the self-assembly of Mn(III)–porphyrin biscarboxylic acid and Co(OAc)₂.