In the title compound, [Ca(C(18)H(15)N(2)O(3)S(2))(H(2)O)(4)]·2C(4)H(10)O, the Ca atom, which lies on an inversion centre, is coordinated octa-hedrally by four water mol-ecules and two anions of the ketene dithio-acetal, the donor atoms of which are the amidic carbonyl O atoms. The central backbone of the ligands (excluding the naphthalene and oxoethyl groups) is essentially planar (r.m.s. deviation 0.035 Å). Intra-molecular hydrogen bonds are observed from the NH group to the formally 'thiol-ate' S atom and from one coordinated water to the nitrile group and to the ether O atom. Inter-molecular hydrogen bonds from the second independent water mol-ecule to the thiol-ate S atom and the side-chain oxo group connect the mol-ecules in chains parallel to the a axis.