CaB2O4 was added into hexagonal boron nitride (hBN) to improve the sintering behaviors of hBN. CaB2O4 and hBN were mixed and then pressed into plates. The plates were sintered at 2000°C for 5h under a N2 ambience. The phase compositions with different CaB2O4 contents were examined with X-ray diffraction analysis. The fracture cross-sections of the hBN plates were investigated by SEM. The apparent density and Rockwell hardness were also measured. The results show that the hBN particles had a plate-like shape and the grain sizes of hBN increased with increasing CaB2O4 contents. The apparent density and Rockwell hardness decreased with increasing CaB2O4 contents. When the CaB2O4 content was 15(wt) %, the hBN has the average grain sizes of 3μm in diameter and 200nm in thickness, the apparent density of 1.06 g/cm3 and the Rockwell hardness of 3, respectively.