There are two 5-amino-1,3,4-thia-diazole-2(3H)-thiolate anions in the asymmetric unit of the title compound, Na(+)·C(2)H(2)N(3)S(2) (-)·2H(2)O, which are almost perpendicular to each other [dihedral angle = 84.64 (6)°]. The two Na(+) cations are in distorted fourfold coordinations by O atoms of the water molecules. The crystal structure is stabilized by N-H⋯S, O-H⋯N and O-H⋯S hydrogen bonds.