The title polymeric compound, [Cd(C(7)H(3)NO(4))(H(2)O)(3)](n) or [Cd(py-2,3-dc)(H(2)O)(3)](n), where py-2,3-dcH(2) is pyridine-2,3-dicarboxylic acid, was obtained by the reaction of cadmium(II) nitrate hexa-hydrate with (pipzH(2))(py-2,3-dc) as a proton-transfer compound in aqueous solution (pipz is piperazine). The mol-ecular structure shows that only the anionic fragment of the starting proton-transfer compound is present in the complex, while the (pipzH(2))(2+) dication has been lost. Each (py-2,3-dc)(2-) ligand bridges two Cd(II) atoms in two different coordination modes, i.e. one end acts as a monodentate and the other end as a bidentate ligand. The three remaining coordination sites on the metal center are occupied by water mol-ecules. The geometric arrangement of the six donor atoms around the Cd(II) atom is distorted octa-hedral. In the crystal structure, O-H⋯O and C-H⋯O hydrogen bonds play an important role in stabilizing the supra-molecular structure.