Abstract: The water-soluble hexaaquacobalt(II) bis(monoethoxyformononetin-3'-sulfonate) tetrahydrate([Co(H2O)6](C18H15O4SO3)2·4H2O) was synthesized using formononetin as lead compound and characterized by IR, 1H NMR, TG-DTA, XRD and single-crystal X-ray diffraction analysis. Single-crystal X-ray diffraction analysis shows that [Co(H2O)6]2+, C18H15O4SO-3 and H2O form several kinds of hydrogen bonds, which consist of the hydrophilic regions of title compound. The isoflavone skeletons are arranged in an anti-parallel fashion, aromatic F-tape and T-tape stacking interactions exist among them, which form the hydrophobic regions of title compound. The sulfo-group is an important bridge as a structural link between the hydrophilic region and the hydrophobic region.The hydrogen bonds, aromatic stacking interactions and the electrostatic interactions between the cation [Co(H2O)6]2+ and the anion sulfonate C18H15O4SO3- lead to the moieties into supramolecule with a three-dimensional structure.