The mol-ecule of the title compound, [CuNa(C(18)H(18)N(2)O(4))(C(2)N(3))(H(2)O)], is almost planar, the maximum deviation from the mol-ecular plane being 0.48 (4) Å. The coordination environment of the Cu(2+) ion is distorted square-planar and it is N(2)O(2)-chelated by the Schiff base ligand. The Na(+) cation has a distorted octahedral environment defined by the four O atoms of the 6,6'-dimeth-oxy-2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolate ligand, a water ligand and a dicyanamide anion.