In the title compound, [Ni(3)(PO(4))(2)(H(2)O)(8)](n), which was synthesized hydro-thermally, all the Ni atoms are located in slightly distorted octa-hedral coordination environments. Two phosphate groups and two Ni atoms share a centrosymmetric four-membered ring and an eight-membered ring such that the four-membered ring is inside the eight-membered ring. The eight-membered rings are connected with the other Ni atoms (lying on centres of symmetry) through phosphate anions, generating a one-dimensional chain structure. Adjacent chains are connected through hydrogen bonds, forming a three-dimensional network.