Abstract: In the fabrication of SiC fibers via preceramic polymer pyrolysis, air-curing is necessary to render the green fiber infusible, but it introduced much oxygen to the fibers, which limited their high-temperature properties greatly. Instead, another promising approach to the preparation of low-oxygen-content SiC fibers has been realized by electron beam (EB) radiation curing under inert atmosphere. This paper studied the influence of EB radiation on the infusibility and thermal stability of polycarbosilane (PCS) fibers and analyzed the mechanism of radiation-curing. The results revealed that the onset-curing dose of PCS fibers was 15MGy and their pyrolysis was similar to that of the air-cured fibers. After pyrolysis up to 1200℃ for 30min under nitrogen atmosphere, inorganic SiC fibers with a lower oxygen content, 3.3wt%, were obtained. Their tensile strength was 1.65GPa, with a microcrystalline size of 3.4nm. After heat-treatment at 1600℃ for 30min under helium atmosphere, they lost 8wt% weight and retained 80% strength, with a grain growth of 12.9 nm.