Bucky onions have been produced by decomposing SiC nanometer powders under high- temperature and vacuum. Transmission electron microscope and high resolution electron microscope observations show that when SiC particles decompose completely, they transform into quasi-spherical hollow carbon particles and onion-like particles composed of concentric graphitic shells. When SiC particles decompose incompletely, they become compound particles, which are composed of β-SiC in particles and of quasi-concentric graphitic shells on surface of particles. The results suggest that the traditional idea that planar graphite is the most stable form of pure carbon would then have to be seriously discussed.