A new method to synthesize Si3N4 nanostructures via catalyst-assisted polymeric precursor pyrolysis is present in this article. The as-prepared nanobelts are single crystals with a uniform thickness and width along the entire length, and contain no detectable defects such as dislocations or stacking faults. The thickness and width of Si3N4 nanobelts range from 40 to 60 run and 600 to 1200 nm, respectively, and the lengths can be up to several millimeters. The growth directions of alpha-Si3N4 nanobelts are [101] and [100]. A solid-liquid-solid and gas-solid reaction/crystallization is proposed for the growth of S3N4 nonastructures.