Boron was introduced into C f /SiC composites as active filler to shorten the processing time of PIP process and improve the oxidation resistance of composites. When heat-treated at 1800°C in N 2 for 1h, the density of composites with boron (C f /SiC-BN) increased from 1.71 to 1.78g/cm 3 , while that of composites without boron (C f /SiC) decreased from 1.92 to 1.77g/cm 3 . So when boron was used, two cycles of polymer impregnation and pyrolysis (PIP) could be reduced. Meanwhile, the oxidation resistance of composites was greatly improved with the incorporation of boron-bearing species. Most carbon fiber reinforcements in C f /SiC composite were burnt off when they were oxidized at 800°C for 10h. By contrast, only a small amount of carbon fibers in C f /SiC-BN composite were burnt off. Weight losses for C f /SiC composite and C f /SiC-BN composite were about 36 and 16wt%, respectively.