The molecules of 8-hydroxyquinolinium-2-carboxylate, C(10)H(7)NO(3), have a planar structure, in which the carboxyl group is ionized and the ring N atom is protonated. The derived nickel(II) complex, bis(8-hydroxyquinoline-2-carboxylato-kappa(3)O(2),N,O(8))nickel(II) trihydrate, [Ni(C(10)H(6)NO(3))(2)].3H(2)O, contains an octahedral central Ni(II) ion coordinated by the hydroxyl O atom, the ring N atom and the carboxylate O atom of each of the two tridentate ligands, with a perpendicular orientation of the quinoline rings.