The asymmetric unit of the title complex, (C(4)H(12)N(2))[Co(C(7)H(3)NO(4))(2)]·4H(2)O, consists of one piperazinediium dication, one [Co(py-2,6-dc)(2)](2-) dianion (where py-2,6-dc is pyridine-2,6-dicarboxyl-ate) and four water mol-ecules. The piperazinediium cation adopts a chair conformation and the Co(II) ion is six-coordinated in an N(2)O(4) environment, having a distorted octa-hedral geometry. In the crystal, inter-molecular O-H⋯O, N-H⋯O and weak C-H⋯O hydrogen bonds link the components, forming a three-dimensional network.