Abstract Dense polycrystalline cBN (Pc BN )–SiCw composites were fabricated by a two‐step method: First, SiO 2 was coated on the surface of cubic boron nitride ( cBN ) particles by the sol‐gel method. Then, silicon carbide whisker (SiC w )‐ coated cBN powder was prepared by carbon thermal reaction between SiO 2 and carbon powders at 1500°C for 2 hour. Then, cBN –SiC w complex powders were sintered by high‐pressure and high‐temperature sintering technology using Al, B, and C as sintering additives. The phase compositions and microstructures of cBN –SiC w composites were investigated by X‐ray diffraction and scanning electron microscopy, respectively. It was found that the SiC w and Al 3 BC 3 had been fabricated by in situ reaction, which cannot only promote densification but also improve mechanical properties. The relative density of Pc BN composites increased from 96.3% to 99.4% with increasing SiC w contents from 5 to 20 wt%. Meanwhile, the Vickers hardness, fracture toughness and flexural strength of as‐obtained composites exhibited a similar trend as that of relative density. The composite contained 20 wt% of SiC w exhibited the highest Vickers hardness and fracture toughness of 42.7 ± 1.9 GPa and 6.52 ± 0.21 MPa•m 1/2 , respectively. At the same time, the flexural strength reached 406 ± 21 MPa.