Carbon nanofibers have been synthesized by the thermal decomposition of acetylene with a copper nanocatalyst derived from cupric nitrate trihydrate at a low temperature of 260 degrees C. The resultant carbon nanofibers were characterized using transmission electron microscopy and X-ray power diffraction. The copper nanoparticles changed from initial irregular shapes to regular shapes during the growth of nanofibers. The copper nanoparticle size has a considerable effect on the morphology of carbon nanofibers. Helical carbon nanofibers with a symmetric growth mode were grown on copper nanoparticles with a grain size less than 50 nm. When the catalyst particle size was in the range of 50-200 nm, straight carbon nanofibers were obtained dominantly. (c) 2008 Elsevier B.V. All rights reserved.