In the title mononuclear complex, [Cd(C12H8N2)(H2O)4]SO4·2H2O, the coordination geometry around the CdII atom is a distorted octahedron, with two aqua ligands occupying the axial positions. Intermolecular O—H⋯O hydrogen bonds lead to the formation of a two-dimensional layer structure parallel to (001). The layers are connected by π–π interactions between the pyridyl and benzene rings of the phenanthroline ligands [centroid–centroid distances = 3.591 (1) and 3.610 (1) Å]
