? Nano SiC–BN composite powders were prepared by dissolving analytically pure H3BO3 and CO(NH2)2 with the mole ratio of 1: 2.5 in the absolute alcohol, adding 80% β-SiC with 0.2 μm average grain size while stirring, firing at 850 ℃ in nitrogen (purity: 99.99%, pressure: 0.92–0.93 MPa) for 15 h. Nano SiC–BN composite specimens were prepared by hot-pressed sintering the nano SiC–BN composite powder in N2 atmosphere with 0.92–0.93 MPa and at 30 MPa axial pressure for 0.5–1 h at 1 750–1 800 ℃. The thermal shock resistance of nano SiC–BN composites was studied by three-point bending, TEM and SEM. The results show that, adding BN can decrease the modulus of elasticity of SiC materials, which improves thermal shock resistance; furthermore, because of the large difference of thermal expansion coefficient between matrix SiC and second phase hexa-BN, thermal mismatch effect results in intercrystalline delamination of h-BN grains and forming many micropores in composite ceramic, which can relax the thermal expansion caused by high temperature effectively, and improve the thermal shock resistance significantly.