The sulfate anion acts as a bridging ligand between the copper(II) ions in the linear polymeric chain of the title compound, [CU(SO4)(C6H6N2O)(2)(H2O)(2)](n). Distorted octahedral coordination about the copper(II) ion is achieved by two ring N atoms of the nicotinamide groups, in a cis conformation [Cu-N 2.016 (3) and 2.018 (3) Angstrom], by two water molecules [Cu-OW 1.986 (3) and 1.989 (3) Angstrom], and by two O atoms of two sulfate ligands [Cu-O 2.418 (3) and 2.421 (3) Angstrom].