Nanosized silicon carbide powders of high purity and low oxygen content have been prepared by thermal chemical vapour deposition (CVD) of dimethyldichlorosilane at pyrolytic temperatures, 1100-1400 degrees C. The nanosized silicon carbide particles prepared at 1400 degrees C consist of small crystallites of beta-SiC arranged randomly in the particles. At pyrolytic temperature below 1300 degrees C, the particles consist of amorphous phase and beta-type SiC crystallites. The average particle size changed from 70 nm to 40 nm and the average size. of the beta-SiC crystallite changed from 7.3 nm to 1.8 nm depending on the pyrolysis conditions. The C/Si molar ratios of the product powders changed from 0.5 to 1.07 with the CVD conditions. The near theoretical values of C/Si molar ratio of the product powders within 0.95-1.05 can be controlled by CVD conditions such as pyrolytic temperature and reactant concentration. Finally, the product powders were characterized by chemical analysis, X-ray diffraction, electron microscopy, and infrared spectroscopy.