The reaction of the sodium salt of 4-nitrobenzoic acid (4-nbaH) with [Ni(H2O)6]Cl2 or [Ni(en)3]Cl2.2H2O (en is ethylenediamine) results in the formation of the known octahedral compound [Ni(H2O)4($\eta^1$-4-nba)2]$.2$H2O (4-nba = 4-nitrobenzoate) 1 or the title compound di(aqua)bis(ethylenediamine) nickel(II) bis(4-nitrobenzoate) 2 respectively. Compounds 1 and 2 were characterized by elemental analysis, infrared spectra, DSC thermograms, weight loss studies and the structure of 2 was determined. Both 1 and 2 can be thermally decomposed to green NiO. The title compound [Ni(H2O)2(en)2](4-nba)2 2 crystallizes in the centrosymmetric monoclinic space group $P2_1/c$ with the Ni(II) situated on an inversion center. The crystal structure of 2 consists of a hexacoordinated Ni(II) complex cation and an uncoordinated 4-nba anion. In the octahedral complex cation, the central metal is linked to two symmetry related bidentate en ligands and two water molecules. In the crystal structure, the cations and anions are linked by three varieties of hydrogen bonding interactions. A comparative study of seven nickel 4-nitrobenzoate compounds is described.