A supramolecular polymer is first constructed through the intermolecular inclusion complexation of bridged bis(permethyl-beta-cyclodextrin) (1) with Mn-III-porphyrin bearing poly(ethylene glycol) (PEG) side chains (Mn-III-TPP) and characterized by UV/vis absorption spectroscopy, NMR, dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM) Mn-III-TPP in the supramolecular polymer 1-Mn-III-TPP would be reduced effectively to a higher electronic spins Mn-II-TPP by sodium ascorbate, but free Mn-III-TPP cannot be reduced in the same condition. The toxicity of the supramolecular polymer in vitro and the magnetic resonance imaging effectiveness both in vitro and in vivo are estimated, and the results obtained not only demonstrate the supramolecular polymer to have no cellular toxicity but also show the MR signal enhancement.