Boron carbide (B4C) additive was adopted to decrease the brittleness of MWCNTs and silicon (Si) containing Al2O3-C refractories through accommodating the formation of ceramic phases. The corresponding phase compositions and microstructures of Al2O3-C refractories were investigated by means of X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The mechanical properties were investigated by means of three-point bending test and the thermal shock resistance was evaluated through traditional water quenching method combined with wedge splitting test. The results show that B4C could favor the growth of in-situ MWCNTs from pyrolysis of resin binder at 800 ℃. Additionally, B4C additive suppresses the SiC formation at 1400 °C attributes to the decreased SiO (g) pressure. In comparison with the Si alone containing refractories, much more residual MWCNTs and in-situ formed MWCNTs contribute to lower brittleness, leading to better thermal shock resistance of B4C and Si containing Al2O3-C refractories.