The structure of the title compound, [Ni(NO₃)(C₁₈H₁₂N₂)(H₂O)₂]NO₃·H₂O, is composed of monomers with the nickel ion octahedrally coordinated to a bidentate biquinoline ligand, a bidentate nitrate anion and two water molecules, and is stabilized by a nitrate counter-ion and a hydrate water molecule. There is a fairly complex hydrogen-bonding scheme involving all the water H atoms and five different nitrate O atoms.