A novel modified cyclodextrin, mono[6-O-6-(4- carboxyl-phenyl)]-β-CD (1), has been synthesized by the reaction of mono[6-(p-toluenesulfonyl)]-β-CD with 4-hydro- xybenzoate, and its molecular self-assembly behavior in both solution and solid state was studied by means of crystallography, NMR spectroscopy and microcalorimetry. The results indicate that the bezoic acid groups are successively penetrated intermolecularly into the adjacent β-CD cavities to form helical columnar supramolecules in the solid state. As compared with crystal, the similar self-assembly behavior of 1 in aqueous solution has also been confirmed by the 1H ROESY spectroscopy. Thermodynamically, the formation of polymeric supramolecules by modified CD in aqueous solution is mainly driven by entropy changes.