ZnO nanowires with variable aspect ratios and microstructures have been prepared by a hydrothermal reaction of Zn foil and Na2C2O4 solution at 140 degrees C. The ZnO nanowires are single crystalline with the wurtzite structure and grow in the [0001] direction, and their aspect ratios and microstructures can be changed by tuning the reaction time and the Na2C2O4 concentration. UV and blue-green emissions that depended on the Na2C2O4 concentration are observed from the ZnO nanowires with different aspect ratios. The photosensitivity of ZnO ultralong nanowires with honeycomb-like micropatterns is found to be about 10 at 5 V. (C) 2009 Elsevier B.V. All rights reserved.