In the title complex, [Co(CHO(2))(2)(C(20)H(14)N(4))(H(2)O)(2)](n), the Co(II) ion, lying on an inversion center, is six-coordinated by two O atoms from two monodentate formate ligands, two N atoms from two 2,6-bis-(pyridin-4-yl)-4,4'-bipyridine (4-pybpy) ligands and two water mol-ecules, displaying an octa-hedral geometry. The 4-pybpy ligand, having a twofold rotation axis, functions in a bridging coordination mode, connecting the Co(II) ions into a corrugated chain along [[Formula: see text]01]. The chains are further linked into a three-dimensional supra-molecular network by O-H⋯O, C-H⋯N and C-H⋯O hydrogen bonds and π-π stacking inter-actions between the pyridine rings [centroid-to-centroid distance = 3.743 (2) Å].