We synthesized ceramic fibers based on silicon carbide (SiC) from polymer blends of polycarbosilane (PCS) and polymethylphenylsiloxane (PMPhS) by melt-spinning and radiation curing. PMPhS was compatible with PCS up to 30 mass%, and formed a transparent melt at temperatures higher than 513 K. The softening point was also lowered by adding PMPhS and 15 mass% of PMPhS to PCS was the most suitable condition for obtaining thin fibers with an average diameter of 14.4 mu m. Due to the lowered softening point of the PCS-PMPhS fibers, gamma-ray curing in air was adopted. The ceramic yield of the cured fiber was 85.5% after pyrolysis at 1273 K. In spite of the small diameter, the resulting tensile strength at 1273 K was rather limited at 0.78 GPa. Blooming of the PMPhS component during pyrolysis may have caused surface defects. After high-temperature pyrolysis at 1673-1773 K, a porous nanocrystalline SiC fiber with a unique microstructure was obtained with surface area of 70-150 m(2)/g. When the fiber was pyrolyzed at the same temperature under a highly reductive atmosphere, wire bundle-shaped fibers were obtained by gas evolution and reactions.