Nanocrystalline aluminum nitride powders were synthesized by introducing high velocity and high temperature aluminum plasma vapor discharge into the nitrogen and ammonia gas mixture. By employing high-current pulse power, aluminum electrodes were explosively vaporized and ionized in a capillary plasma device to generate the metal plasma vapor. The effect of ammonia addition on the AlN content and average particle size in reacting gas has been studied by various techniques of material characterization such as XRD, XPS, and TEM. At the nitrogen/ammonia volume ratio of 50:50, synthesized nanopowders was found to be free of aluminum metal and the content is pure AlN nanopowders in the form of hexagonal phase. The smallest average particle size of 8 nm and highest content of AlN was achieved at 100% ammonia composition. (c) 2005 Elsevier B.V. All rights reserved.