SiC nanowires were synthesized in large quantity by heating SiO and activated carbon fibers without metal catalysts. The morphologies of product were studied by SEM and TEM and it indicated that the SiC nanowires obtained at the bottom of the activated carbon fibers surfaces were coated by an amorphous silicon oxide layer and the core of SiC nanowires were measured, typically as about 8-20 nm in diameter, while in situ formed nanotree-bud network, Y-junction and the "S" shape nanostructure were observed in those SiC nanowires obtained at the up of the activated carbon fibers surfaces. These SiC/SiO2 heterostructure, particularly novel 2-D heterostructure, would be expected as important blocks in building nanodevices and as reinforcement in advanced composites. (c) 2005 Elsevier B.V. All rights reserved.