A SiO2 nanolayer, 1.02.8 mass% in content, was coated on cubic boron nitride (cBN) powder by rotary chemical vapor deposition (RCVD). The morphology of the SiO2 nanolayer changed from isolated islands to a continuous layer with increasing supply rate of the precursor, tetraethyl orthosilicate. The effect of the SiO2 coating on the sinterability and mechanical properties of cBN for machine-tool applications was evaluated. The SiO2-coated cBN (cBN/SiO2) powder was mixed with Al2O3 and consolidated by spark plasma sintering (SPS) at 14731873 K. The phase transformation temperature of cBN to hexagonal BN (hBN) in Al(2)O(3)cBN/SiO2 was 1773 K, 100 K higher than that in Al(2)O(3)cBN composites. The highest density of the Al(2)O(3)cBN/SiO2 composites was 99.5% at 30 vol% cBN/SiO2 content, at which the microhardness and fracture toughness were 28 GPa and 4.1 MPa center dot m1/2, respectively. This indicates that RCVD-deposited SiO2 is a promising sintering aid for cBN and Al(2)O(3)cBN/SiO2 sintered bodies produced by SPS may be applicable as cutting tools.