The zinc oxide (ZnO) thin films were deposited onto the glass substrates by a novel chemical method, which is based on the alternate dipping of substrate in an alkaline zinc nitrate solution and double-distilled water containing H2O2 (1%) at room temperature. The time duration for which the substrate is dipped in the precursor solution, plays an important role and it has been shown in this work that the time period for which a substrate is dipped in dilute H2O2 solution, which we referred as reaction period, affects significantly on the structural, surface morphological and optical properties. The structural analyses from X-ray diffraction (XRD) patterns displayed the formation of polycrystalline ZnO with no preferred orientations. The scanning electron micrographs (SEM) revealed the spongy and powdery clusters for low reaction period, which was converted to uniform spherical grains with increase in reaction period. The optical band gap was found to be declined from 3.28 to 3.12eV with increase in reaction period. (c) 2007 Elsevier B.V. All rights reserved.