ZnO thin films were deposited on nesa silica glass substrates via sol-gel method using Zn(CH3COO)(2).2H(2)O-Co(CH3COO)(2) .4H(2)O-polyvinylpyrrolidone (PVP)-diethanolamine-2-methoxyethanol solutions. The effects of the Co2+ ions and PVP in coating solutions on the photoanodic properties of the resultant films were studied by measuring photocurrent potential curves and action spectra in a three-electrode cell with a supporting electrolyte of pH = 9.18. The photoanodic current under xenon lamp light decreased with increasing amount of Co2+ ions due to the decreased quantum efficiency in the UV regions. The photoresponse was extended to wavelengths of ca. 450 nm when the Co/Zn mole ratios were 0.05 and 0.15, while the response to the visible light diminished at Co/Zn > 0.3. The UV photoresponse of Co2+-free ZnO films increased when PVP was added in the coating solutions, where the maximum quantum yield of 0.62 was obtained at a wavelength of 364 nm. On the other hand, the UV photoresponse rather decreased when PVP was added in Co2+-containing solutions. (C) 2003 Kluwer Academic Publishers.