An nanoparticles were synthesized by polyol process with sodium bicarbonate (NaHCO3) as a pH-buffering agent. The introduction of NaHCO3 to polyol process made it possible to lower the reaction temperature and shorten the reduction time. In this study, the effects of the NaHCO3/Au weight ratios and the PVP concentrations on the reduction rate of AlCl4- and the particle size of An nanoparticles were investigated. The NaHCO3/Au weight ratio was varied from 0.2 to 10. The reduction rate of AuCl4- was observed by the speeds of the color changes of the mixtures. UV-vis spectra and electron microscopic images indicated that the size of An nanoparticles was determined by the NaHCO3/Au weight ratios and the PVP concentrations. (c) 2005 Elsevier B.V. All rights reserved.