Ultra long SiC core and SiO2 shell nanocables have been prepared by pyrolysis of poly (dimethyl siloxane) at 1050℃ in flowing Argon. The longest nanocable can be up to at least 6mm. Transmission electron microscopy observations indicate that the diameter of the cores varies from about 3 to 18nm, and the thickness of the outer sheaths varies from about 6 to 45nm and that the cores are crystalline and the sheaths are amorphous. The growth of the nanocables may be governed by a chemical vapor solid process. The nanocables exhibit good photoluminescence property.