Carbon fiber was reacted with gaseous silicin monoxide which is produced from pack-powder mixture at elevated temperature. As a result of the reaction, two kinds of SIC fiber were obtained. The first one was SiC fibers which were converted from carbon fibre. THe fiber is constituted with polycrystal like fine grains or monolithic crystals that have a size from sub-micron to 10. their size depends on the temperature during the conversion reation. The second one was ultre-fine Sic fiber that were found on the surface of the converted SiC fibers.