A thin film of copper(I) oxide (thickness similar to 9 Angstrom), grown on a Cu(III) crystal, was used as a model photocatalyst for decomposition of D2O using ultraviolet light (hv 1.55-6.21 eV). No evidence for water photosplitting was observed. The experimental uncertainties establish an upper limit of 2 x 10(-21) cm(2) for the cross section of the photoprocess sought. The pure Cu2O film was grown by bombardment with O-2(+) ions (1.5 kV) at a sample temperature of 605 K and was characterized by Auger electron spectroscopy.