The asymmetric unit of the title compound, [Ni(C(3)H(10)N(2))(2)(H(2)O)(2)](C(4)O(4))·4H(2)O, contains one-half of the diaqua-bis(1,3-propane-diamine)nickel(II) cation, one-half of the centrosymmetric squarate anion and two uncoordinated water mol-ecules. In the cation, the Ni(II) atom is located on a crystallographic inversion centre and has a slightly distorted octa-hedral coordination geometry. The six-membered chelate ring adopts a chair conformation. O-H⋯O hydrogen bonds link the cation and anion through the water mol-ecule, while N-H⋯O hydrogen bonds link the cation and anion and cation and water mol-ecules. In the crystal structure, inter-molecular O-H⋯O and N-H⋯O hydrogen bonds link the mol-ecules into a three-dimensional network structure.