The title compound {systematic name: bis(μ2-dihydrogen 4-azaniumyl-1-hydroxybutane-1,1-diphosphonato)bis[aqua(dihydrogen 4-azaniumyl-1-hydroxybutane-1,1-diphosphonato)nickel(II)] dihydrate}, [Ni2(C4H12NO7P2)4(H2O)2]·2H2O, was synthesiized under hydrothermal conditions. Its structure is isotypic with the CoII analogue. The crystal structure is built up from centrosymmetric dinuclear complex molecules and the structure is reinforced by a net of intermolecular O—H...O and N—H...O hydrogen bonds. One water molecule is bound to the NiII atom in the octahedral coordination sphere, while the second is part of the intermolecular hydrogen-bond system.