The asymmetric unit of the title compound, [Cu(C2H8N2)2(H2O)2](C11H11N4O2S)2, contains one sulfamerazinate anion in a general position and one half-cation that is located on a center of inversion. The Cu(II) cation shows a strong Jahn-Teller distortion. It is coordinated by four N atoms of two ethyl-enedi-amine ligands in the basal plane and two O atoms at much longer distances in the axial positions in a bipyramidal coordination. In the crystal, the building blocks are connected by N-H⋯N, O-H⋯N, N-H⋯O and O-H⋯O hydrogen bonding into a two-dimensional network parallel to (001).