The title compound, [Ni(H(2)O)(6)][Ni(3)(C(7)H(3)NO(4))(4)(H(2)O)(4)]·8H(2)O, was obtained by the reaction of nickel(II) nitrate hexa-hydrate with pyridine-2,6-dicarb-oxy-lic acid (pydcH(2)) and 1,10-phenanothroline (phen) in an aqueous solution. The latter ligand is not involved in formation of the title complex. There are three different Ni(II) atoms in the asymmetric unit, two of which are located on inversion centers, and thus the [Ni(H(2)O)(6)](2+) cation and the trinuclear {[Ni(pydc)(2)](2)-μ-Ni(H(2)O)(4)}(2-) anion are centrosymmetric. All Ni(II) atoms exhibit an octa-hedral coordination geometry. Various inter-actions, including numerous O-H⋯O and C-H⋯O hydrogen bonds and C-O⋯π stacking of the pyridine and carboxyl-ate groups [3.570 (1), 3.758 (1) and 3.609 (1) Å], are observed in the crystal structure.