In the title compound, [Ni(C(10)H(6)NO(3))(2)(H(2)O)(4)], the central Ni(II) atom is located on an inversion center and coordinated in a slightly distorted octa-hedral geometry by two O atoms from two 2-oxo-1,2-dihydro-quinoline-4-carboxyl-ate ligands and four water mol-ecules, all of which act as monodentate ligands. The crystal structure features an extensive network of inter-molecular hydrogen-bonding inter-actions (O-H⋯O and N-H⋯O) and offset face-to-face π-π stacking inter-actions [centroid-centroid distances = 3.525 (3) and 3.281 (5) Å].