Abstract: SiBN(C) ceramic fibers have been certificated as a promising candidate for reinforced body in ceramic matrix composites, due to their excellent properties high temperature stability, high temperature creep resistance behavior as well as high temperature oxidation resistance etc. The thermal stability and microstructure of SiBN(C) ceramic fibers were analyzed. Moreover, the high temperature anti-oxidation process of SiBN(C) ceramic fibers was investigated at temperature range from 1 100 ℃ to 1 500 ℃, and the influence of carbon content on the dielectric properties of SiBN(C) ceramic fibers was also investigated. The results show that the SiBN(C) ceramic fibers treated upon thermally heating after 1 600 ℃ in N₂ atmosphere retard amorphous structure. The HT-TGA results show that the SiBN(C) caramic fibers have good high temperature thermal stability, and mass loss of the ceramic fibers is only 1.5wt% (1 450 ℃, N₂ atmosphere). Furthermore, SiBN(C) ceramic fibers show pronounced high-temperature oxidation resistance. The oxidized ceramic fibers with dense and crack-free structure are observed, moreover, the ceramic fibers still remain amorphous structure after oxidation treatment at 1 400 ℃ for 5 h in air, whereas the XRD analysis shows that oxidized samples start to occur skin-core structure and crystallize at 1 500 ℃ for 5 h. Moreover, the results of XRD and SEM associated with EDX show the majority of the oxidated sample surface is the crystallization of cristobalite. The dielectric property investigation of SiBN(C) ceramic fibers show that, dielectric constant and dielectric loss of SiBN(C) ceramic fibers are 2.1 and 0.001 7 (frequence is 10 GHz), respectively, when the C content is as low as 0.1wt%. The properties evaluation indicate the SiBN(C) ceramic fibers indeed satisfy the requirements that proposed as reinforcement of high temperature wave-transparent materials.