The growth of GaN nanowires (NWs) proceeded at 900 degrees C by chemical vapor deposition with two systems of (GaCl3 + NH3) and (Ga2Cl4 + NH3) on 850 degrees C-preannealed Au-, Ni-, Au/Ni-, and Ni/Au-covered substrates was investigated. GaCl3 and Ga2Cl4 had different interactions with solid Ni catalyst droplets and their growths of GaN NWs were different. Au and bilayer catalysts of Au/Ni and Ni/Au became liquefied during the GaN growth and had similar catalytic capabilities with their different Ga precursors. Catalyst droplets with low viscosity interrupt the growth of GaN NWs for the Au-catalyzing system. Our bilayer catalysts of Au/Ni and Ni/Au provide a consistent and reliable approach to grow long and smooth GaN NWs with a uniform diameter distribution. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3526975] All rights reserved.