The asymmetric unit of the title polymeric mononuclear Cu(II) complex, [Cu(C2N3)2(NH3)2] n , contains one half-mol-ecule, the complex being completed through inversion symmetry, with the Cu(II) atom situated on the centre of symmetry. The coordination polyhedron around Cu(II) is a Jahn-Teller-distorted [CuN6] octa-hedron. The terminal N atoms of two dicyanamide ligands and two ammine ligands form an approximate square plane, with N-Cu-N bite angles of 89.72 (5) and 90.28 (5)°. The coordination polyhedron is completed in the axial positions by the central amide-type N atoms of two additional dicyanamide ligands, with an elongated Cu-N distance of 2.548 (1) Å. In turn, each of the four dicyanamide ligands, acting as bidentate, link the Cu(II) ions into a two-dimensional polymeric structure parallel to (100). The ammine H atoms are involved in inter-molecular hydrogen bonding with the free terminal N atoms of neighbouring dicyanamide ligands, yielding a three-dimensional network.