Nanocrystalline gold octahedrons were synthesized in an aqueous environment via the reduction of HAuCl4 by ascorbic acid with the addition of NaOH. Highly monodisperse octahedral particles with controlled sizes ranging from 20 to 40 nm were prepared in high-yield by varying the reaction temperature. The structural and optical properties of the synthesized gold nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. The prepared nanoparticles exhibited efficient surface-enhanced Raman scattering (SERS) properties, and their SERS activities were highly size-dependent. (C) 2008 Elsevier B. V. All rights reserved.