In the crystal of the title compound, [Ni(NO(3))(2)(C(18)H(10)N(4))(H(2)O)]·H(2)O, the Ni(II) ion is coordinated in a distorted octahedral geometry by two N atoms of the 1,10-phenanthroline moiety of the ligand, three O atoms from two nitrate anions and an O atom from one water mol-ecule. O-H⋯O hydrogen bonds between the coordinated and the solvent water molecules and between these water molecules and the nitrate O atoms help to establish the crystal packing.