The preparation and chemical properties of barium-oxocuprat (I) inclusive the results of the crystal structure determination by single crystal X-ray investigations are described. BaCu2O2 crystallizes isotypically with SrCu2O2 . (a = 5.72 and c = 10.06 Å. Spacegroup : D194h - 141/amd.) The influence of the bigger Ba2⨁-ion on the oxigenconfiguration surrounding the cations is discussed. It seems that the stretched O - Cu - O-dumbell is an invariable structural element in the oxocompounds of copper (I), which is shown by comparison of already known oxocuprates (I) . Only the way of interchainment varies evidently with stoichiometry.