In the title mononuclear complex, [Cd(C(12)H(8)N(2))(H(2)O)(4)]SO(4)·2H(2)O, the coordination geometry around the Cd(II) atom is a distorted octa-hedron, with two aqua ligands occupying the axial positions. Inter-molecular 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 inter-actions between the pyridyl and benzene rings of the phenanthroline ligands [centroid-centroid distances = 3.591 (1) and 3.610 (1) Å].