ZnO nanorods have been grown onto indium thin oxide (ITO) coated glass substrates by electrochemical deposition technique using oxygenated zinc chloride solutions at the bath temperature of 80 degrees C and pH value of 5.8. The effect of the galvonostatic pretreatment process according to the size of the ZnO nanorods has been examined. The pretreatment consists of the formation of ZnO seed layers at different currents of -1.0 mA and -2.0 mA by the galvonostatic process and then the subsequent ZnO nanorods had been produced using the potentiostatic mode at the potential of -1.0 V. ZnO nanorods produced on the seed layers exhibited different morphological, structural, and optical properties. X-ray diffraction results showed that ZnO nanorods are highly crystalline and wurtzite hexagonal phase with preferred orientation along (002) direction. The energy band gaps were found to be 3.50 eV, 3.52 eV and 3.60 eV without and with the seed layer of -1.0 mA and -2.0 mA respectively. Atomic Force Microscopy (AFM) images revealed that the ZnO nanorods deposited on the ITO-coated substrates without and with the seed layer are composed of rod-shaped grains with a cross hexagonal section perpendicular to the substrate. The average diameters of the ZnO nanorods were found to be 560 +/- 16.78 nm, 450 +/- 32.12 nm and 370 +/- 18.46 nm without and with the seed layer of -1.0 mA and -2.0 mA respectively. The SEM images have shown that the lengths of the ZnO nanorods varied between 1.0 mu m and 2.0 mu m. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.