We successfully synthesized four kinds of NiO from 1D to 3D as follows: NiO nanowires, nanosheets, nanobulks and nanospheres. With our careful preparation and accurate reagent ratio, different and beautiful morphologies were obtained through the hydrothermal process only by changing the active agent. We mainly chose NiC2O4 center dot 2H(2)O as the precursors of NiO and found that the existence of ethylene glycol (EG), polyethylene glycol (PEG) and glycine played an important role in synthesis of disparate NiO nanostructures. The gas-sensing performances of the as-prepared NiO nanostructures with different dimensions were investigated toward ethanol at 350 degrees C. NiO nanowires present the better gas sensing properties and the corresponding response value (R-g/R-a), response time and recovery time were about 3.4, 4s, and 5 s to 50 ppm ethanol, respectively. (c) 2012 Elsevier Ltd. All rights reserved.