By using a potentiostatic electrodeposition method, well-aligned ZnO nanorod arrays (ZNAs) were synthesized under different conditions. The effects of preparing conditions on the electrodeposition of ZNAs were systematically studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and absorbance spectroscopy. It is indicated that the electrodeposition parameters, such as electrodeposition potential, electrolyte pH, concentration of precursors, temperature of solution and electrodeposition time, have significant influence on the morphology, diameter, density and growth rate of ZNAs. The ZNAs, with well-defined crystallization, can be only obtained when the applied potential is controlled from -0.4 to -1.0V. The growth temperature has great impact on the morphology of ZnO nanostructure but it is weakly related to the band gap (Eg) of ZNAs. The rod diameters can be monitored to some extent only by changing the concentration of the precursors. The electrolyte pH value has relative influence on the diameter of ZNAs. With the growth time increasing, ZNAs with high aspect ratio can be gained.