The PCBN (polycrystalline cubic boron nitride) composites were synthesized by mixing cubic boron nitride micropowders with Ti and Al micropowders at a certain mass ratio under high temperature and ultra-high pressure conditions. Phase composition and microstructure of the samples were analysed by X-ray diffraction and scanning electron microscopy. The effects of sintering temperature on the mechanical properties and microstructure of the PCBN ceramics were investigated. It was shown that BN, AlN, TiN and TiB2 phases coexist in the PCBN ceramics fabricated at ultra-high pressure (5.5GPa) and high temperature (1400-1500?C). With the increase of sintering temperature, pores and gaps inside the PCBN composites gradually disappeared and densified structure was formed. The best comprehensive mechanical properties of the PCBN composites were obtained at 1500 ?C with a flexural strength of 1009MPa and microhardness of 35.8GPa.