Radical polymerization of vinyl monomers was performed in nanochannels of porous coordination polymers with unsaturated metal sites, [M(1,3,5-benzenetrisoenzoate)] (1AI, M = Al3+; 1Eu, M = Eu3+; 1Nd, M = Nd3+; 1Y, M = Y3+; 1La, M = La3+; and 1Tb, M = Tb3+). In this system, the polymerization behaviors are strongly dependent on the Lewis acidity of the metal sites. For example, polymerizability of monomers was influenced by the metal sites because of the interaction with the monomers. From the viewpoint of streteoregularity, composition of isotactic unit in the resulting poly(methyl methacrylate) (PMMA) increased as the Lewis acidity of the hosts becomes higher. Although discrete Tb3+ ions are not effective for changing the stereoregularity of PMMA in solution polymerization system, nanochannels of 1Tb gave PMMA with the increase in the isotactic unit, showing that the metal ions embedded in the pore walls of PCPs are useful for controlling stereoregularity of polymers.