Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO 2 nanolayer (abbreviated as cBN/Ni and cBN/SiO 2 , respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO 2 powder by spark plasma sintering at 1473–1973K for 0.6ks. The effects of Ni and SiO 2 coatings on the densification, phase transformation of cBN and hardness of SiO 2 –cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973K in SiO 2 –cBN/SiO 2 composites, 300K higher than that in SiO 2 –cBN/Ni composites, indicating that SiO 2 retarded the transformation of cBN. The relative density of SiO 2 –cBN/SiO 2 with 50vol% cBN sintered at 1873K was 99% with a hardness of 14.5GPa.