In the title complex, [Ni(C(8)H(9)N(2)O(4))(2)(H(2)O)(2)]·4H(2)O, the Ni(II) ion is coordinated in a slightly distorted octa-hedral environment formed by two bis-chelating H(2)pimda (H(3)pimda is 2-propyl-1H-4,5-dicarb-oxy-lic acid) ligands and two coordinated water mol-ecules. In the crystal structure, a three-dimensional framework is formed by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds involving the solvent water mol-ecules, coordinated water mol-ecules, carboxyl-ate O atoms and the protonated N atoms of the H(2)pimda ligands. The propyl groups of each H(2)pimda ligand are disordered over two sets of sites with refined occupancies of 0.50 (2):0.50 (2) and 0.762 (11):0.238 (11). In one water solvent mol-ecule, one of the H atoms was refined as disordered over two sites of equal occupancy.