The Physical and photo-electrochemical properties of CuO grown on microcrystalline silicon thin films (mu c-Si:H) by heating copper film were investigated. The Raman spectrum for mu c-Si: H exhibits a peak at 520 cm(-1) confirming its good crystallinity with a crystalline volume fraction of 91%. The X-ray diffraction pattern shows narrow peaks with a monoclinic symmetry. The indirect optical transition (1.19 eV) is well matched to the solar spectrum and the low transmittance (< 7%at 400 nm), indicating a good optical quality. The capacitance measurements, performed in Na2SO4 electrolyte indicate that CuO/mu-Si:H electrode acts as n-type semiconductor with a donor density N-D of 4.88 x 10(19) cm(-3) implying the existence of oxygen vacancies in the film. The potential of its conduction band (-0.563 VSCE) made up of Cu-eg orbital, is more cathodic than the O-2/O-2(+) level (-0.3 V-SCE), but not enough to yield O-2 reduction under solar light. By contrast, the electrons in the Cu2+: 4 s level excited by the UVA of the solar radiation, leading to oxidation of 26% of RhB (10 ppm) mainly by the O-2(+) radicals within 60 min.