In this Letter, we report the synthesis of hexagonal crystalline BN powders with novel cage-like structures from a single-source precursor NH4BF4 at 400-600 degrees C for 12 h. The obtained samples are characterized by XRD, XPS, TEM and HRTEM. Experiments reveal that the as-prepared BN powders exist in multiwall nanocages with dimensions from about 20 to 200 nm and have very good anti-oxidation properties at high temperatures. (c) 2005 Elsevier B.V. All rights reserved.