Ultrafine (u.f.) silicon carbide (SIG) particles were synthesized from SiOx (x=0, 1, 2) silicon (Si), silicon monoxide (SiO), or silica (SiO2)) powders (1.0 - 3.0 mu m) and acetylene (C2H2) in an electric furnace operated under an argon (Ar) atmosphere. The particle products were analyzed by scanning electron microscopy, X-ray diffraction analysis and thermogravimetry-differential thermal analysis. The u.f. particles (25 - 35 nm) of cubic WC (beta-SiG) could be produced through Si+C2H2, SiO+C2H2 or SiO2+C2H2 reaction. SLC selectivity was 43% for the Si/C2H2 system (C2H2/Si=1.5), 79% for the SiO/C2H2 system (C2H2/SiO=1.2), and 51% for the SiO2/C2H2 system (C2H2/SiO2=2.0). The tendency of the experimental results on SiC selectivity for the SiO/C2H2 system coincided with the theoretical curve based on thermodynamic equilibrium calculations.