Si3N4 nanobelts and nanodendrites were simultaneously synthesized via a novel catalyst-assisted crystallization of polymer-derived amorphous silicon carbonitride. The single crystal nanobelts, with a uniform cross-section of 20-30 nm in thickness and 100-300 nm in width, can grow up to a few millimeters in length. The nanodendrites consist of a plate-like stem and nanobelts branches of 10-20 nm thick and 50-150 nm wide. The branches that are up to 50 mu m in length grew only along the middle line of the stem with regular spacing. A growth for both nanobelts and nanodendrites is attributed to a solid-liquid-gas-solid process. (c) 2004 Published by Elsevier B.V.