The crystal structure of the title compound, [Cu(OH2)2(phen)] (SO4) (phen = 1,10-phenanthroline), has been determined by single-crystal X-ray diffraction methods at room temperature, being refined by full matrix least-squares methods to a residual of 0.033 for 1445 'observed' reflections. Crystals are monoclinic, C2/c, a 14.883(8), b 13.843(9), c 7.019(4) Ŭ ߠ108.60(4)ꬠZ 4. As in a number of other copper(II) and nickel(II) derivatives with (CuL4)(SO4) stoichiometry, the pseudo-square planar copper environments [Cu-N,O: 2.009(2), 1.970(2) Šin the present case] are bridged through the two axial coordination positions by sulfate groups: O.SO2.O[Cu(OH2)2(phen)]O.SO2.0, etc. to give a linear polymeric array [Cu-O(SO4), 2.468(3) ŝ; a crystallographic twofold axis passes through the copper atom.