Several types of Si-based ceramic fibers have been prepared using an organic-to-inorganic conversion process. In this article, the preparation, microstructure, and high-temperature stability of SiC-based ceramic fibers prepared from polycarbosilane of an organosilicon polymer are reviewed. The first fiber produced was an amorphous Si-C-O fiber, next was a low-oxygen content Si-C fiber, and finally, a nearly stoichiometric SiC fiber was developed. These fibers are continuous fine fibers that have high tensile strength with high heat resistance. The pyrolytic behavior and active-passive oxidation of these fibers at high temperatures are described here. The heat resistance of these fibers increases in the order of the Si-C-O fiber, the Si-C fiber, and the SiC fiber. The high-temperature properties are dependent on the atomic arrangement and the quantity of amorphous SiC_xO_y and glassy carbon in the fibers. Possible applications for these fibers are as refractory materials, and as reinforcement fibers for plastics, metals, and ceramics.