Nanocrystalline boron nitride (BN) was synthesized via a simple route by the reaction of sodium borohydride with sodium azide in an autoclave at 600 degrees C. X-ray powder diffraction pattern indicated that the product was hexagonal BN, and the cell constant was a = 2.495 angstrom, c = 6.687 angstrom. Transmission electron microscopy image showed that it consisted of whisker-like particles with an average size of 200 nm x 20 nm. The product was also studied by FT-IR, XPS and TGA. It has good thermal stability and oxidation resistance in high temperature. (c) 2006 Elsevier Ltd. All rights reserved.