The effects of B4C addition and heat treatment temperature on the microstructure, mechanical properties and oxide resistance of SiC-based composite ceramics were investigated. The results show that the addition of B4C can improve the crystallinity and graphitization of SiC. The linear change rate of SiC-based composite ceramics decreases from 1.39% to 0.58%. The flexural strength and compressive strength are increased by 1.8 times and 2 times (i.e., from 28.06 MPa to 50.25 MPa and from 48.03Pa to 98.58 MPa), respectively, after heat treatment at 1 450 ℃ at B4C addition of 6% (in mass fraction). The oxidation index of SiC-based composite ceramics decreases from 30.33% to 18.35% after oxidation at 1 400 ℃, and the thickness of the oxide layer decreases substantially from 3.52 mm to 0.23 mm with the increase of B4C addition from 0 to 6%. Therefore, adding B4C can enhance the amount of SiC whiskers and the strength and oxidation resistance of SiC-based composite ceramics as well.