A water-soluble metallo-supramolecular polymer MSP-f-6Np, which possesses a regular pore aperture of 1.4 nm, has been assembled from a structurally flexible naphthalene-appended [Ru(bipy)3]2+ complex and cucurbit[8]uril. As the first periodic metallo-supramolecular polymer formed by a flexible building block, MSP-f-6Np exhibits a hydrodynamic diameter of 122 and 164 nm at 0.1 and 2.0 mM of the monomer concentrations. Synchrotron small angle X-ray scattering experiments confirm that MSP-f-6Np possesses porosity periodicity in both the solution and solid states. Compared with a control, the new highly ordered porous system displays enhanced photocatalytic activity for the degradation of organic dyes.