Nanocrystalline porous ZnO films are deposited onto alumina foil substrates by polymer-modified spray pyrolysis of zinc nitrate and zinc acetate solutions. The dependence of the concentration of added ethylcellulose and the type of zinc precursor on both the photocatalytic properties and films morphologies is investigated. It is established that the addition of ethylcellulose as a modifier in the spray solution leads to the formation of a porous structure with crystallites sizes about 15 nm, when zinc acetate is used as precursor. These films show better photocatalytic activity for degradation of Malachite Green (MG) dye than the films obtained from zinc nitrate modified solution. The zinc nitrate films exhibit weaker activity for degradation of MG regardless of their smaller crystallite size (8-12 nm). This can be explained with their lower porosity than that of polymer-modified zinc acetate films. It is established that 450 degrees C is the limit temperature of treatment for the preparation of ZnO films with good photocatalytic activities. This photocatalytic activity in films shows a drop in the comparison to the films treated at lower temperature, due to decreasing of the pore number and deterioration of the surface morphology. (C) 2010 Elsevier B.V. All rights reserved.